CHARACTERIZING SERVICE LEVELS ON AN ELECTRONIC NETWORK

[0001] Applications are often deployed in data centers, where the applications execute on one or more servers. A data center generally has a network that includes a number of different network devices, such as various types of routers, switches, etc. A failure of any individual network device can sometimes cause the application to be unavailable from outside the data center. Thus, from the perspective of an end user, the availability of an application is dependent not only on whether the application itself is executing properly, but also on the proper functioning of intervening network devices that connect the application to the end user.

[0002] To address this issue, network devices may be deployed in redundant pairs or larger groups. Redundant network devices and/or links can provide some measure of protection against individual device failures or link failures, because when an individual device/link in a given group fails, the other device will sometimes continue functioning and, therefore, the application may still be reachable by end users. Thus, whether a particular application is reachable from outside the data center depends not only on the proper functioning of the individual network devices, but also on how effective the redundant groups are at preserving connectivity when one or more devices in the redundant groups fail.

[0003] The above listed example is intended to provide a quick reference to aid the reader and is not intended to define the scope of the concepts described herein.

[0004] This document relates to processing electronic data. One implementation is manifest as a technique that can include obtaining events from one or more event logs. The events can reflect failures by one or more network devices in one or more data centers. The technique can also include filtering the events using one or more criteria to obtain a sub-set of the events. The technique can also include determining one or more network stamps of an application, characterizing one or more service levels of individual network devices in the one or more network stamps using the sub-set of the events, and characterizing a service level of the application based on the service levels of the individual network devices in the one or more network stamps.

[0005] Another implementation is manifest as one or more computer-readable storage devices comprising instructions which, when executed by one or more processing devices, cause the one or more processing devices to perform acts. The acts can include obtaining events from one or more event logs. The events can reflect failures by one or more network devices in one or more data centers. The acts can also include filtering the events using one or more criteria to obtain a sub-set of the events and characterizing one or more service levels of the network devices using the sub-set of the events. The acts can also include determining one or more correlations of the service levels and identifying one or more risky devices based on the one or more correlations.

[0006] Another implementation is manifest as a system that can include an event analysis component and one or more processing devices configured to execute the event analysis component. The event analysis component can be configured to obtain events from event logs, the events reflecting failures on a network by one or more network devices in one or more data centers. The event analysis component can also be configured to characterize a service level of an application or a network device based on the events, and to identify one or more recommended potential network changes to change the service level of the application or the network device. The one or more recommended potential network changes can be recommended based on at least one of expected costs or expected benefits associated with the recommended potential network changes.

[0013] This discussion relates to characterizing service levels of devices or applications on an electronic network. For the purpose of this document, the term “service level” includes concepts such as reliability, availability, traffic flow/loss, etc. For example, availability relates to the fraction of time a given application, device, or hardware/software component is functioning on average over a given period of time, e.g., the “uptime” as measured on a time basis, such as an annual basis. Reliability relates to the likelihood of failure of a given application, device, or hardware component, e.g., the expected time until the next failure. Failure relates to instances when a given application, device, or component does not perform as intended.

[0014] Specific definitions of availability, reliability, and failure can be found in various references. Although the following definitions are not explicitly adopted herein, the following definitions may provide further clarity for the terms availability, reliability, and failure. For example, MIL-STD 721C defines availability as a measure of the degree to which an item is in an operable and committable state. MIL-STD 721C defines reliability as (1) the duration or probability of a failure-free performance under stated conditions or (2) the probability that an item will perform its intended function, without failure, for a specified interval under stated conditions. Failure can be defined as the inability of an item to function within its specified limits of performance (MIL-STD 721B) or as an event or inoperable state in which any item or part of any item does not or would not perform as previously specified (MIL-STD 721C).

[0015] Generally speaking, the disclosed implementations may characterize the service level of an individual network device, such as an access router, aggregation switch, etc. Additionally, the disclosed implementations may characterize the service level of an application that uses one or more network devices. The service level of an application can be a function of the service level of the network devices used by the application. Moreover, some of the network devices may be deployed in redundant groups of multiple devices. Thus, the service level of an application can be a function of how effective the redundant groups are at ensuring that application traffic can be routed without significant impact despite failures, e.g., some alternative path along alternative devices/links. The term “network service level” describes the service level of an application independently of failures of application code and/or computing devices executing the application, and relates to the service level of various network devices and links upon which an application depends for connectivity. For example, network service levels can be impacted by hardware failures (device or link failures), software failures (protocol, device operating system, firmware, etc.), as well as configuration failures. The term “network availability” is similarly independent of application code failures and failures of computing devices executing the application.

[0016] Some of the present techniques can leverage data center event logs, which may include events that are logged by various devices or applications. The events in the log can include error reports indicating failure of one or more devices in the data center. Event logs can be processed to evaluate the service levels of individual devices in the data center. In some implementations, the event logs can be filtered to provide a more compact data set for evaluating service levels, e.g., by filtering out duplicate events, merging simultaneous events, etc.

[0017] FIG. 1 illustrates an example of a data center network architecture 100. The architecture can be manifest in a data center 102 that is connected to a network 104, such as the Internet. In this case, the architecture 100 includes devices or components such as one or more core routers 106, one or more access routers 108, one or more aggregation switches 110, one or more top-of-rack (ToR) switches 112(1) and 112(2), and one or more racks 114(1), 114(2), 114(3), and 114(4). Each of the racks 114 can include one or more server devices that host an application 116. Note that different instances of the various devices in FIG. 1 are distinguished by parenthetical references, e.g., 112(1) refers to a different ToR switch than 112(2). When referring to multiple devices collectively, the parenthetical will not be used, e.g., ToRs 112 can refer to either or both of ToR 112(1) or ToR 112(2). Note also that architecture 100 can include various devices or components not shown in FIG. 1, e.g., various intrusion detection and prevention systems, virtual private networks (VPNs), firewalls, load balancers, etc.

[0018] From a logical standpoint, the architecture 100 can be organized into a hierarchy that includes a core layer 118, an L3 aggregation layer 120, and a L2 aggregation layer 122. This logical organization can be based on the functional separation of Layer-2 (e.g., trunking, VLANs, etc.) and Layer-3 (e.g., routing) responsibilities. In FIG. 1, only one access router 108 and one aggregation switch 110 are shown, but examples with multiple access routers and multiple aggregation switches follow. In implementations with multiple access routers, the multiple access routers can be deployed in redundancy groups to provide redundancy at the L3 aggregation layer 120. Likewise, in implementations with multiple aggregation switches, the multiple aggregation switches can be deployed in redundancy groups to provide redundancy at the L2 aggregation layer 122. Generally, in a redundancy group, the group contains multiple members and individual members can perform the switching/routing functions when other member(s) of the redundancy group fail. Note also that FIG. 1 illustrates core routers 106 in a redundant configuration. While the following examples use redundant pairs of devices to explain certain inventive concepts, devices can be redundantly configured in groups of 2 or more. Thus, the term “group” as used herein encompasses both pairs of devices as well as larger groups.

[0019] Generally speaking, redundancy groups can be deployed in various configurations, including “active-standby” configurations and “active-active” configurations. In active-standby configurations, one or more devices are active (e.g., carrying traffic) and one or more other devices are on standby (e.g., not carrying traffic) and can be activated to take over for a failing device. In active-active configurations, the devices in the group are active and, when a device in the group fails, traffic that would have otherwise been carried by the failing device can be carried by the remaining members of the group.

[0020] ToRs 112 (also known as host switches) connect the servers hosted by the racks 114 to a remainder of the architecture 100 via an internal data center network represented by connecting lines in FIG. 1. Host ports in these ToR switches are often 10/100/1000 Ethernet, with the uplinks being Gigabit Ethernet or 10GE ports. The ToRs can be connected upstream to aggregation switch 110. These aggregation switches can serve as an aggregation point for Layer-2 traffic and typically support high-speed technologies such as 10 Gigabit Ethernet to carry large amounts of traffic (e.g., data).

[0021] Traffic from the aggregation switch 110 can be forwarded to the access router 108. The access router can use Virtual Routing and Forwarding (VRF) to create a virtual, Layer-3 environment for each tenant. (A tenant is an application, such as a service, hosted on servers which use network devices for connectivity—route traffic from/to users or other services to/from its hosted servers.) Thus, FIG. 1 illustrates a single tenant, application 116, although multiple tenants can execute on individual servers of racks 114. In some implementations, the L3 aggregation layer 120 can aggregate traffic from up to several thousand servers and route the traffic to core routers 106 that can connect to the rest of the architecture 100 and network 104.

[0022] Some implementations (especially user-facing applications) may use load balancers to improve the performance of hosted applications. Redundant pairs of load balancers can connect to the aggregation switch 110 and perform mapping between static IP addresses (exposed to clients through DNS) and dynamic IP addresses of the servers to process user requests to application 116. Load balancers can support different functionalities such as network address translation, secure sockets layer or transport layer security acceleration, cookie management, and data caching.

[0023] Firewalls can be deployed in some implementations to protect applications from unwanted traffic (e.g., DoS attacks) by examining packet fields at IP (Internet Protocol) layer, transport layer, and sometimes even at the application layer against a set of defined rules. Generally, software-based firewalls can be attractive to quickly implement new features. However, hardware-based firewalls are often used in data centers to provide performance-critical features.

[0024] Virtual private networks can augment the data center network infrastructure by providing switching, optimization and security for web and client/server applications. The virtual private networks can provide secure remote access. For example, the virtual private networks can implement secure sockets layer, transport layer security, or other techniques.

[0025] Considering FIG. 1, note that there are several points of failure which could result in the unavailability of application 116. For example, application 116 could have a software failure, hardware failure, misconfiguration, protocol error, or other malfunction that causes application 116 to stop executing properly on the servers of racks 114. Additionally, failure of both ToRs 112(1) and 112(2) can result in unavailability of application 116, as can concurrent failure of both of the redundantly-configured core routers 106. Note also that, since there is only a single aggregation switch 110 and a single access router 108 shown in FIG. 1, a failure of either of these individual devices could be sufficient to prevent users from accessing application 116 from outside data center 102.

[0026] For the purposes of this document, the network devices on which a given application depends to carry application traffic are referred to as the “network stamp” of the application. Thus, in FIG. 1, the network stamp of application 116 includes ToRs 112(1) and 112(2), aggregation switch 110, access router 108, and core routers 106. The following discussion will explain techniques for characterizing the service level of an application based on the network stamp of the application. In some implementations, the characterization of the service level can reflect redundant groups of network devices. Detailed examples are discussed herein with respect to the L2 aggregation layer 122 and the L3 aggregation layer 120. However, those skilled in the art will understand that these concepts are readily extensible to other network devices or layers of the network topology (e.g., core router redundancy, load balancer redundancy, etc.)

[0027] As a hypothetical example, for purposes of exposition, assume network 104, core routers 106, access router 108, aggregation switch 110, ToRs 112(1) and 112(2), racks 114(1)-114(4), and software of application 116 all exhibit perfect reliability—no failures ever. Also assume that application 116 is not hosted elsewhere and is only available via data center 102. Under this idealized set of circumstances, application 116 would exhibit 100% availability and infinite reliability. Now, assume that access router 108 is replaced with a device having 90% availability instead. Because there is no redundancy at the L3 aggregation layer 120, the availability of the application is now reduced to 90%. Note also that replacing aggregation switch 110, instead of access router 108, with a device having 90% availability would have a similar effect on the availability of application 116.

[0028] More generally, to compute network availability for a given application, network availability can be considered on an end-to-end basis for each component (link or device) carrying application traffic. Some implementations may assume statistical independence of failures among devices. Under such an assumption, if both aggregation switch 110 and access router 108 have 90% availability, the expected network availability of application 116 is (0.9*0.9)=0.81 or 81%. As discussed in more detail below, further implementations may consider the extent to which device failures are statistically correlated.

Data Center Example with L3 Redundancy

[0029] FIG. 2 illustrates data center 102 with a different architecture 200, e.g., in a different configuration to provide redundancy at the L3 aggregation layer 120. In FIG. 2, multiple access routers 108 are now deployed as a redundancy group, in this case, a redundancy pair. Thus, the difference between the network stamp of application 116 in FIG. 1 and FIG. 2 is the addition of an additional access router 108 in a redundant configuration in FIG. 2. The changes to the network stamp of application 116 can have different effects on the availability of application 116, as discussed more below.

[0030] Continuing with the hypothetical example introduced above, assume network 104, core routers 106, aggregation switch 110, ToRs 112(1) and 112(2), racks 114(1)-114(4), and software of application 116 all exhibit perfect reliability and 100% availability. Further, assume each individual device from access routers 108 exhibits 90% availability, and that a single access router can handle all of the application traffic in the event that the other access router fails (otherwise the remaining access router will drop traffic when the traffic is redirected to the remaining access router). The following scenarios illustrate how the effectiveness of the redundancy may vary depending upon whether failures of the individual access routers are closely correlated.

[0031] In one “zero redundancy” hypothetical circumstance, the addition of redundancy at the L3 aggregation layer 120 provides no additional benefit relative to a single, 90% available access router 108. Specifically, consider the case where the individual devices of access routers 108 always fail together. Under these circumstances, the availability of application 116 is still 90%, since the redundant pair of access routers 108 effectively still functions as a single point of failure.

[0032] Now, consider a different “perfect redundancy” hypothetical circumstance where the individual redundant access routers 108 never fail together. In this circumstance, the availability of application 116 is 100%. Hypothetically, two redundant access routers with perfect redundancy, i.e., never failing together, could provide 100% availability with only 50% availability for each individual device. Continuing with the hypothetical example, in a redundant group of 3 access routers 108, the individual devices need only exhibit availability ⅓ of the time, a group of 4 devices needs ¼ availability, etc.

[0033] In practice, redundant devices are not likely to provide zero redundancy or perfect redundancy. Rather, sometimes the individual devices in a redundant group will fail together, e.g., due to a common cause such as a power outage at a location where the redundancy group is located. Other times, some of the devices in the redundancy group will fail while other devices in the group continue functioning properly. For example, a power supply for one device in a redundancy group may fail causing one device in the group to fail. The following discussion explores techniques for characterizing application and device service levels in view of these practical considerations.

[0034] As mentioned above with respect to FIG. 1, one practical approach used in some implementations is to assume statistical independence of failures. Here, given the assumptions above, the hypothetical network availability is the probability that at least one access router is available.

Pr (at least 1 access router is available)=1−Pr (no access router is available)=1−Pr (access router 1 isn't available)*Pr(access router 2 isn't available)=1−(1−0.9)*(1−0.9)=1−(1−0.9)̂2=1−0.01=0.99

[0035] Thus, using redundancy, higher system availability can be achieved even though the individual components of the system have lower availability of 0.9 each. More generally, the equation:

Pr (at least 1 access router available)=1−(1−Pr (access router failing))̂# of access routers

can be used to generalize to different numbers of access routers. The equation can be generalized in a straightforward manner to other device types/links/numbers of data centers as well.

[0036] For example, the previous examples illustrate the notion of intra-data center redundancy, e.g., redundancy of devices or links within a given data center. Some implementations may consider service levels of inter-data center redundancy as well, e.g., circumstances where applications are hosted at multiple data centers. Inter-data center redundancy can be considered when evaluating the service level of an application in a manner similar to that set forth above. Thus, for example, the expected availability of an application hosted at two data centers with availability of 90% each is 99%, assuming statistical independence of failures by the two data centers and that each data center is individually capable of carrying the necessary application traffic.

Data Center Example with L2 and L3 Redundancy

[0037] FIG. 3 illustrates an architecture 300, where data center 102 is in a different configuration to provide redundancy at both the L3 aggregation layer 120 and the L2 aggregation layer 122. In FIG. 3, a pair of aggregation switches 110 are now deployed as a redundancy group at the L2 aggregation layer 122 and are coupled to the redundant pair of access routers 108 in L3 aggregation layer 120. Thus, the difference between the network stamp of application 116 in FIG. 2 and FIG. 3 is the addition of an additional aggregation switch 110 in a redundant configuration in FIG. 3. Again, the changes to the network stamp of application 116 can have different effects on the availability of application 116 depending on the extent to which various device failures may be correlated.

[0038] Note that, in the example of FIG. 3, each aggregation switch 110 is connected to both access routers 108 from the redundant pair. Thus, as long as at least one access router 108 at the L3 aggregation layer 120 and one aggregation switch 110 at the L2 aggregation layer 122 is functioning, traffic can pass between ToRs 112(1) and 112(2) and core routers 106. This change to the network stamp of application 116 can have different effects on the availability of application 116, as discussed more fully below.

[0039] For example, consider another hypothetical scenario where network 104, core routers 106, ToRs 112(1) and 112(2), racks 114(1)-114(4), and software of application 116 continue to exhibit perfect reliability and 100% availability. Furthermore, assume that, collectively, the redundant group of access routers 108 at L3 aggregation layer 120 provides perfect redundancy—at least one of the two devices in the pair is always functioning properly and can handle the application traffic should the other device fail. In this hypothetical, the only point of failure is at the pair of aggregation switches 110 in L2 aggregation layer 122.

[0040] The “zero redundancy” hypothetical mentioned above with respect to the introduction of redundancy at the L3 aggregation layer 120 also applies to the redundant L2 aggregation layer 122 shown in FIG. 3. That is, if the individual aggregation switches in the redundant pair always fail together, there is no benefit to having multiple aggregation switches. Likewise, the “perfect redundancy” hypothetical also applies, e.g., if the individual aggregation switches 110 never fail together and can handle each other's application traffic, the availability of application 116 is 100%.

[0041] Moreover, note also that failures may occur at multiple layers and whether these failures tend to co-occur can affect the availability of application 116. Continuing with the hypothetical, assume that both the redundant pair of access routers 108 and the redundant pair of aggregation switches 110 exhibit 90% availability, e.g., 10% downtime. In other words, both access routers in the redundant pair are down 1 out of every 10 hours on average, and both aggregation switches in the redundant pair are down 1 out of every 10 hours. Note that, in a best-case hypothetical scenario, the failures of the redundant pairs at the L2 and L3 layers always occur together. Thus, the availability of application 116 is still 90%, because the failures always co-occur. In a worst-case scenario, the failure of the L2 layer may never co-occur with the L3 layer. In this case, the availability of application 116 is 80%, i.e., for every 10 hours of operation, one hour is lost to failure of the redundant aggregation switches at L2 and another is lost to the failure of the redundant access routers at L3.

[0042] For similar reasons as already discussed, neither the best-case scenario nor worst-case scenario is likely. Rather, sometimes the redundant pair of access routers will fail at the same time as the redundant pair of aggregation switches, and other times both devices in one pair will fail whereas at least one device in the other pair will continue functioning. Assuming statistical independence, the expected availability is 0.9*0.9 or 0.81 (81%). Since failures may or may not be statistically independent, some implementations may consider the extent to which failures at one layer may be correlated to failures at other layers when characterizing the service level of application 116.

[0043] FIG. 4 shows an exemplary system 400 that is consistent with the disclosed implementations. As shown in FIG. 4, system 400 includes network 104 connecting numerous entities, including a data center 102(1) and a data center 102(2), a server operations center 402 having a monitoring system 404, an analysis device 406 having an event analysis component 408, and a client device 410 having an application interface 412.

[0044] Network 104 can include various wired and/or wireless networks and combinations thereof. For example, network 104 can include the public Internet as well as various private networks or portions thereof that connect any of the devices/data centers shown in FIG. 4. For the purposes of the following discussion, it is generally sufficient that network 104 provides connectivity between devices or data centers that share information.

[0045] Each data center 102 can be configured as discussed above with respect to any of FIGS. 1-3, or in other suitable configurations. Client device 410 can interact with application 116 by communicating over network 104 with either data center 102(1) or data center 102(2). Application interface 412 can include logic for communicating with application 116, e.g., formatting functionality, display functionality, etc. For example, client device 410 can be employed by an end user that wishes to use various features made available by application 116.

[0046] Server operations center 402 can generally include one or more server devices configured to monitor the individual data centers for network problems. For example, monitoring system 404 can execute on the server devices to monitor data centers 102(1) and 102(2). In some implementations, network operators (e.g., network engineers) at server operations center 402 may attempt to resolve issues on either data center, and can track the issues using support tickets, diaries, or other techniques.

[0047] Event analysis component 408 of analysis device 406 can be configured to analyze various events in one or more data centers, e.g., to characterize the service level of various applications located at data center 102(1), 102(2), or both. The event analysis component can also be configured to characterize the service level of one or more network devices at one or both data centers. Generally speaking, the event analysis component 408 can be configured to analyze various events as well as support tickets and other data to characterize the service levels of applications and/or devices.

[0048] Note that the various devices shown in system 400 are illustrated with respect to logical roles that can be performed by the devices in operation of system 400. However, the geographical locations of the various devices are not necessarily reflected by system 400. For example, data centers 102(1) and/or 102(2) may be collocated with server operations center 402 and/or analysis device 406. As another example, the event analysis component 408 and/or monitoring system 404 can be implemented on one or more devices inside an individual data center, e.g., on one or more of server racks 114.

[0049] Furthermore, note that FIG. 4 illustrates server operations center 402 as multiple server devices whereas analysis device 406 and client device 410 are illustrated as individual computing devices. This reflects one particular implementation, and other implementations may provide characterization functionality and/or client functionality as discussed herein via multiple devices. Likewise, server operations center and/or data center functionality as discussed herein may be performed by individual devices.

[0050] In addition, functionality described herein with respect to a particular device or devices can be distributed across multiple devices or combined on a single device. For example, monitoring system 404 and event analysis component 408 can be collocated at a server operations center on a single device or multiple devices. As another example, the event analysis component and/or monitoring can be employed on a device at one or both data centers of system 400.

[0051] Further note that, in practice, there may be additional instances of each computing device mentioned herein, e.g., additional analysis devices, server operations centers, client devices, and data centers. As discussed in more detail below, each of the computing device(s) shown in FIG. 1 can include one or more processing devices, such as computer processors, executing instructions stored on one or more computer-readable storage media such as volatile or non-volatile memories, optical disks, hard drives, flash drives, etc.

[0052] The monitoring system 404 on server operations center 402 can generally serve to obtain various data relating to the operation of data centers 102(1) and 102(2). The obtained data can be provided to event analysis component 408 for further processing, as discussed in more detail below. For example, the data obtained by the monitoring system can include events, trouble tickets, maintenance data, and traffic data.

[0053] With respect to events, the monitoring system can accept event log streams (e.g., from syslog) and can perform functions such as reformatting and filtering event data based on rules and routing messages to any installed rule engines or archival log files. For example, the event logs can be obtained from, and include events generated by, network devices such as core routers 106, access routers 108, aggregation switches 110, and/or ToRs 112 as well as various other network devices (firewalls, load balancers, etc.). The events in the event logs can contain information about what type of network component experienced an event, the event type, the other end-point of this component (e.g., the one-hop directly-connected neighbor), and a short machine-generated description of the event.

[0054] The monitoring system 404 on server operations center 402 can also obtain trouble tickets or data related to trouble tickets. For example, network operators may troubleshoot network faults through problem tracking systems or “ticketing” systems that coordinate among network operators working on the problem. Some troubleshooting systems can be built around a Request for Comments memo (e.g., RFC 1297) containing specifications for trouble ticket systems for network operations centers (“NOCs” such as server operations center 402). In such a case, a (possibly unique) identifier herein referred to as NOC TicketID is assigned to each failure event. These tickets contain structured information about when and how an event was discovered and diaries of steps taken by the network operators in troubleshooting and mitigating the problem.

[0055] The monitoring system 404 on server operations center 402 can also obtain maintenance data. For example, network operators can use a maintenance tracking and revision control system to track activities that can change the network such as device provisioning, configuration changes, and/or software upgrades throughout the system 400. The maintenance tracking and revision control system can be features of the monitoring system 404 or a separate system. Before debugging an outage, a network operator can check the maintenance tracking system for on-going and planned maintenance. The network operator can use the revision control system to detect any recent changes to the device configuration files. Maintenance data obtained from the maintenance tracking and revision control system can reflect the device provisioning, configuration changes, and/or software upgrades.

[0056] The monitoring system 404 on server operations center 402 can also obtain traffic data. For example, traffic carried on network interfaces (links) can be logged using Simple Network Management Protocol (“SNMP”) polling that averages traffic seen every five minutes, for example. Other sources of traffic data can be obtained from sampling based approaches such as sFlow. Traffic monitoring systems can use the MIB format to store the data that includes fields such as the interface type (token ring, Ethernet etc.), the other end of the interface, the interface status (up/-down), timestamp, and/or the number of bytes sent or received by the interface, among others.

[0057] Using the monitoring system 404 as described above, the server operations center 402 may allow network operators to monitor status of the data centers 102(1) and 102(2) for various failures, e.g., a failed router, improper device configuration, slow response times, etc. Individual events obtained by the monitoring system can be processed to characterize service levels of applications and/or devices as discussed in more detail below.

[0058] Event analysis component 408 can utilize event logs obtained by the monitoring system 404 to characterize application and/or device service levels. For instance, additionally or alternatively to the event logs obtained from the monitoring system, the event analysis component can utilize data collected by network operators. For example, network operators can detect faults from network devices and analyze root causes by using monitoring alarms, such as syslog and SNMP traps, and by monitoring device status via ping and SNMP polling. The event analysis component can obtain other device-related data to use in analyzing service levels of both applications and devices, including trouble tickets, maintenance data, and traffic data.

[0059] Event analysis component 408 can correlate the above mentioned data with failure events in the event logs to extract failures impacting network traffic and to reverse-engineer the topology information using link-level connectivity as the topology changes from time-to-time. As used herein, a failure can be thought of as an event that causes a device or a link to be unavailable to perform its intended task (e.g., carry traffic). Specifically, a link failure can be thought of as occurring when the connection between two devices is down. Similarly, a device failure can be thought of as occurring when the device is not functioning for routing/forwarding traffic.

[0060] Some implementations of event analysis component 408 can filter several types of spurious network events in event logs, such as inaccurate event logs, duplicate events caused by multiple devices reporting the same event, single events being recorded as multiple events, and “shadow” reports (e.g., chatty devices). In regard to inaccurate event logs, syslog messages can be spurious with devices sending multiple notifications that are logged as failure events even though a device is operational. In regards to multiple reporting devices, two or more devices (e.g., neighbors) may send notifications for the same event that are logged as separate events leading to redundant event logs (e.g., multiple redundant error reports). The error reports can be thought of as redundant if subsequent error reports relate to an error that was reported by an earlier error report. Regarding a single event being recorded as multiple events, a flapping device can generate multiple down and up messages which each get logged as different events.

[0061] Shadow events can be thought of as events being triggered due to devices which are being scheduled for replacement or have been detected as faulty by operators but which are awaiting repairs. In some cases this effect can be severe with some devices (e.g., “chatty” or “shadow” devices) sending more than a thousand device down notifications over a few hours because the notification system did not suppress them during the troubleshooting window. Techniques that the event analysis component 408 can employ to filter several types of spurious events from network event logs are described in more detail below. The filtered network event logs can be used by the event analysis component to characterize application and/or device service levels as discussed herein.

[0062] FIG. 5 shows event analysis component 408 embodied on analysis device 406. The analysis device is one example of a system that can be configured to accomplish certain concepts, as discussed in more detail below. In this case, the analysis device is illustrated as a desktop computer. The terms “computer” or “computing device” are used interchangeably, and as used herein can mean any type of device that has some amount of processing capability. While specific examples of computers are illustrated for purposes of explanation, other examples of such computers can include traditional computing devices, such as personal computers, any of the devices introduced relative to FIGS. 1-4, cell phones, smart phones, personal digital assistants, or any of a myriad of ever-evolving or yet to be developed types of devices. Further, a system can be manifest on a single computing device or distributed over multiple computing devices.

[0063] In this case, analysis device 406 can include an application layer 502, an operating system layer 504, and a hardware layer 506. The event analysis component 408 can be manifest as a program or application of the application layer 502, among other configurations. In this example, the event analysis component can include a filter module 508, a characterization module 510, and an output module 512. The event analysis component can process data, such as event logs, provided over network 104 by monitoring system 404. Alternatively, monitoring system 404 can populate a database 522 with event data and the event analysis component can process the event data in the database.

[0064] The hardware layer 506 can include a processor 514, storage/memory (e.g., one or more computer-readable storage media) 516, a display device 518, and/or various other elements. For instance, the other elements can include input/output devices, optical disc readers, USB ports, etc.

[0065] Processor 514 can execute computer-readable instructions to provide a functionality, such as an event analysis component functionality. Data and/or computer-readable instructions can be stored on storage/memory 516 and/or received from another source, such as optical storage device 520. The storage/memory 516 can include any one or more of volatile or non-volatile memory devices, hard drive storage devices, flash storage devices (e.g., memory sticks or memory cards), and/or optical storage devices (e.g., CDs, DVDs, etc.), among others.

[0066] Alternatively to the illustrated configuration of analysis device 406, the computer can employ a system on a chip (SOC) type design. In such a case, functionality provided by the computer can be integrated on a single SOC or multiple coupled SOCs. For instance, the computer can include shared resources and dedicated resources. An interface(s) can facilitate communication between the shared resources and the dedicated resources. As the name implies, dedicated resources can be thought of as including individual portions that are dedicated to achieving specific functionalities. Shared resources can be storage, processing units, etc., that can be used by multiple functionalities.

[0067] Generally, any of the functions described herein can be implemented using software, firmware, hardware (e.g., fixed-logic circuitry), manual processing, or a combination of these implementations. The term “engine,” “tool,” “component,” or “module” as used herein generally represent software, firmware, hardware, whole devices or networks, or a combination thereof. In the case of a software implementation, for instance, these may represent program code that performs specified tasks when executed on a processor (e.g., CPU or CPUs). The program code can be stored in one or more computer-readable storage/memory devices, such as computer-readable storage media. The features and techniques of the component are platform-independent, meaning that they may be implemented on a variety of commercial computing platforms having a variety of processing configurations.

[0068] As used herein, the term “computer-readable media” and “computer-readable medium” can include signals and hardware. In contrast, the terms “computer-readable storage media” and “computer-readable storage medium” exclude pure signals. Computer-readable storage media can include “computer-readable storage devices”. Examples of computer-readable storage devices include volatile storage media, such as RAM, and non-volatile storage media, such as hard drives, optical discs, and flash memory, among others.

[0069] In some implementations, the filter module 508 can be configured to perform functionality relating to separating duplicate events from a remainder of events in one or more event logs. The filtered events can result in a sub-set of germane events that are used as a dataset for characterizing device or application service levels. The characterization module 510 can be configured to perform functionality relating to characterizing current or future service levels of individual network devices and/or applications at data centers 102(1) and/or 102(2). For example, the characterization module can be configured to characterize the service levels using individual events from the filtered sub-set of events as well as ticket data, maintenance data, and/or traffic data. The characterization module can infer relationships between the ticket data, maintenance data, and/or traffic data and the events based on time of occurrence, date of occurrence, duration of occurrence, physical location, type, property, configuration setup, and/or functional role of the involved devices. The output module 512 can be configured to output results of the characterizing. The output results can include values reflecting the characterized service levels (e.g., a percentage availability of a device or application). The output results can also identify various devices or device groups that tend to fail together, e.g., “risky” devices or device groups.

[0070] In the example of FIG. 5, the output module 512 can generate GUI screenshot 524 by obtaining data from monitoring system 404 and/or database 522. As mentioned, database 522 can be populated by the monitoring system and can include events from one or more data centers. Events obtained from, or relating to one or more data centers can be thought of as a dataset that is evaluated by the event analysis component 408. The event analysis component can separate individual events relating to network devices and links connecting these devices from those of other data center devices. The event analysis component can also determine the network stamp of an application, e.g., on a data center-by-data center basis and characterize the service level of the application based on the service levels of individual devices in the network stamp.

[0071] The GUI screenshot 524 shown in FIG. 5 can be generated by the event analysis component 408 from the dataset. GUI screenshot 524 illustrates that, at data center 102(1), application 116 has approximately 98% availability. At data center 102(2), application 116 has approximately 96% availability. The event analysis component 408 can infer these percentages using the individual network stamps of application 116 at the individual data centers, as discussed in more detail herein, including the various hypothetical examples. In other words, FIG. 5 illustrates a configuration where the network stamp of application 116 at data center 102(1) has 98% availability whereas the network stamp of application 116 at data center 102(2) has 96% availability.

[0072] To summarize, several features that can be offered by the event analysis component 408 are described above and below. These features can include characterizing device and/or application service levels. Another feature, discussed in more detail below, can involve identifying risky redundancy groups, e.g., redundancy groups of one or more devices that tend to fail together instead of individually. A further feature can involve evaluating the effectiveness of redundancy when a redundancy group has multiple devices and also evaluating the effectiveness of redundantly hosting an application at multiple data centers. These features are described in more detail below.

[0073] As mentioned above, some implementations employ filtering of events from event logs to obtain a dataset that can be used to characterize service levels of applications and/or devices. FIG. 6 shows a filtering method 600 for separating a sub-set of germane events from less informative events from a set to obtain a sub-set. This method can utilize events from various sources. In this case, the events can be manifest as Syslog/SNMP events 602 and can be filtered using tickets from a NOC ticket database 604. In this implementation, obtained events that do not have an associated NOC ticket can be removed by a “no ticket” filter at 606. This filter can be based upon the assumption that if an event was not dealt with by an operator, then it is likely that the event did not cause an impact. Thus, filter 606 can filter events based on associated ticket criteria relating to whether the events have associated NOC tickets.

[0074] The method can employ a timing filter 608 that filters events using timing-related criteria. The timing filter can be used to fix various timing inconsistencies. In one implementation, the timing filter can first group events with the same start and end time originating on the same interface into a single event. This process can remove duplicate events. Next, the timing filter can pick the earliest start and end times of multiple events that originated within a predefined time window on the same interface. For example, any events that happened within a predefined time of 60 seconds on the same interface can be grouped into a single event (e.g., characterized as a single event). This process can reduce or avoid any problems due to clock synchronization and log buffering. The timing filter can also be used to group two events using interface criteria, e.g., by identifying events that originate on the same interface. For example, events that have the same start time but different end times can be grouped into a single event that is assigned the earlier of the end times. The earliest end times can be utilized since events may not be marked as cleared long after their resolution.

[0075] The technique can employ a planned maintenance filter 610 that applies planned maintenance criteria. Events caused by planned maintenance can have less value in understanding device behavior than unplanned events (e.g., unexpected outages). Thus, the planned maintenance filter can remove events that are caused by planned maintenance activities.

[0076] The technique can employ a shadow device filter 612. The shadow device filter can apply shadow device criteria to filter events logged by devices that are scheduled for replacement or that have been detected as faulty by operators but are awaiting repairs. The shadow device filter can identify these shadow devices by arranging the devices in the descending order of their number of failures. In one implementation, for a top percentage of the devices in this list, all events are merged that have the same “NOC TicketID” field. This constitutes a merged event reflecting individual events with the same ticket ID that are likely to have the same symptoms. In one case the top percentage is defined as the top five percent, but other values can be employed in other implementations.

[0077] The technique can employ an impact filter 614 that applies impact criteria to filter events. An event can be defined as having an impact when the event affects application reliability e.g., throughput loss, number of failed connections or increased latency. In implementations without access to application-level logs, failure impact can be estimated by leveraging network traffic data 616 and computing the ratio of the median traffic on a failed device/link during a failure and its value in the recent past. For example, the value of the recent past can be set as the preceding eight-hour (or other duration) time correlation window 618. Other implementations can use other values. A failure has impact if this ratio is less than one, or another (e.g., lower) threshold on the ratio can be used. The above acts can collectively allow method 600 to identify the failures with impact at 620. Note that other filters can alternatively or additionally be utilized.

[0078] As mentioned above, some implementations may characterize the service level of an application hosted at one or more data centers. FIG. 7 shows a method 700 that can be applied in this context. For example, method 700 can be performed by event analysis component 408 to characterize the service level of an application.

[0079] At block 702, the method can obtain a set of events logged at one or more data centers. In one implementation, the set of events can be obtained from a data center monitoring system or from a database that stores the set of events on behalf of the data center monitoring system. The events can reflect failures by one or more network devices in the one or more data centers.

[0080] At block 704, the method can filter the events using one or more criteria. For example, the method can separate spurious and duplicate events to obtain a filtered sub-set of the events using method 600. In one implementation, the separating can be accomplished by applying a pipeline of event filters to the set of events to generate the filtered sub-set of the events. In some cases, the pipeline can be created by selecting individual filters from a set of available event filters. The individual event filters may each apply different criteria to filter different events to create the filtered sub-set.

[0081] At block 706, the method can determine one or more network stamps of an application. For example, each data center hosting an application can have an individual network stamp. In some cases, block 706 can include processing the filtered sub-set of events to determine the network stamp of the application in the data centers.

[0082] At block 708, the method can characterize the service level of one or more network devices in the network stamps. For example, the method can characterize the availability, reliability, and/or traffic loss of an individual access router, aggregation switch, etc. In addition, the method can characterize the service levels of the one or more network devices by characterizing the service level of a redundant group that includes multiple network devices.

[0083] At block 710, the service level of the application can be characterized using the service levels of the network devices, e.g., the service levels of individual devices and/or redundant groups of devices in the network stamp(s) where the application is hosted. In implementations where the application is hosted on a single data center, the service level can be the availability of the network stamp at the single data center. In implementations where the application is hosted on multiple data centers, the service level can be a function of availability of the application on each of the multiple data centers. Some implementations may assume statistical independence of the availability of the application on different data centers.

[0084] At block 712, the method can identify potential network changes relating to the application or network devices. For example, the method can identify a redundant configuration for the application based on one or more criteria, e.g., hosting the application at multiple data centers, adding a new redundancy group to a given layer of a network stamp, etc. As another example of a network change, the method can identify a suggested change to the ToR connectivity of one or more aggregation switches. In some implementations, the suggested change can be identified to meet a constraint, such as a service level agreement (“SLA”) defined metric relating to reliability, availability, traffic loss, etc.

[0085] Note also that cost can be used as criteria for identifying potential network changes. For example, cost in terms of currency, time, resources, etc., can be determined for each potential change. For example, hosting an application at a new data center may cost approximately $10,000,000 and be expected to increase network availability of the application from 90% to 99.9%. Merely adding a redundant device to a data center where the device is already hosted may cost approximately $10,000 and be expected to increase network availability of the application from 90% to 99%. Depending on the specific requirements for application availability, either approach may be appropriate.

[0086] Further implementations may recommend one or more of the identified potential network changes using a cost-benefit analysis. For example, some implementations may recommend the least expensive potential network change that is expected to meet a given constraint such as an SLA requirement while excluding other potential network changes that are not expected to meet the constraint. Other implementations may rank various potential network changes on a cost-per-unit of availability (or reliability) expected to be obtained by making the respective network changes. A top-ranking subset can be recommended while discarding other, less cost-efficient possible changes. Additionally, some implementations may fix a cost budget and select one or more recommended changes that meet the cost budget. The recommended potential changes can include those changes that meet the cost budget and tend to maximize the expected service level. Other potential changes that do not meet the budget can be excluded from the recommended potential changes.

[0087] Note that some implementations may focus the service level of the application from a network-stamp perspective. In other words, such implementations may disregard the consequences of application code failure and/or failure of servers or racks hosting the application, and instead focus on the service levels provided by the network devices used by the application to communicate with other devices outside the data center. However, further implementations may characterize the service level of the application based on both the service level of the network stamp(s) of the application as well as the service levels of the application code and/or hosting servers/racks. The following discussion focuses on characterizing application service levels from a network stamp perspective, e.g., “network service levels.”

[0088] In some implementations, the network stamp of an application can be determined by considering the connections between the various devices in an individual data center. Considering the example of FIG. 8, which shows an architecture 800 where data center 102 is configured with a second application 802. Note that application 116 is shown as hosted on two server racks 114(1) and 114(2) connected by a single ToR 112(1) through pairs of redundant aggregations switches 110(1), access routers 108(1), and core routers 106. Application 802 is shown as hosted in a similar configuration but with a single aggregation switch 110(2) and a single access router 108(2), also note that application 802 is hosted on racks 114(3) and 114(4) and connected via ToR 112(2).

[0089] Note also that each application can be viewed as part of a common tree of devices that includes all of the devices in the data center. The individual application network stamps can include devices that are in different subtrees. In FIG. 8, application 116 has a subtree rooted at access routers 108(1) that is distinct from a second subtree rooted at access router 108(2) for application 802. The core routers are typically shared across multiple hosted applications and, therefore, in some implementations the core routers are not considered part of the application-specific network stamp.

[0090] In some implementations, a network operator can manually evaluate the physical and/or logical connections of the data center configuration to determine the network stamp of each application. For example, the network operator could identify ToR 112(1), aggregation switch pair 110(1), access router pair 108(1), and core router pair 106 as the network stamp of application 116. Likewise, the network operator could identify ToR 112(2), aggregation switch 110(2), access router 108(2), and core routers 106 as the network stamp of application 802.

[0091] In further implementations, application traffic can be leveraged to determine the network stamp of the application. For example, event analysis component 408 can evaluate traffic flows through the data center to determine through which devices application traffic flows (e.g., inbound or outbound network traffic). The event analysis component can also extract redundant device groups from the traffic by identifying individual devices that have common parents or children. For example, the event analysis component can infer from network traffic that individual aggregation switches of aggregation switch pair 110(1) are redundantly paired to ToR 112(1), because traffic to/from ToR 112(1) passes through both aggregation switches in the pair. As another example, since traffic from both aggregation switches 110(1) passes through both access routers 108(1), the event analysis component can infer that the access routers are redundantly paired with one another. The event analysis component can also infer that, since the network traffic from ToR 112(2) goes through single aggregation switch 110(2) and single access router 108(2), there is no redundancy for single aggregation switch 110(2) or single access router 108(2). Note that failure of a non-redundant device can cause the entire subtree rooted at the failed device to become unavailable due to loss of connectivity.

[0092] Some implementations may infer certain naming conventions that convey whether devices are redundantly paired. For example, access router pair 108(1) may include an individual access router named AR1_A and another individual access router named AR1_B. In contrast, individual access router 108(2) may be simply named AR2. In this instance, the naming convention suffix “_A” and “_B” imply two redundant devices that have the common prefix “AR1.” Further implementations may infer redundancy by considering both traffic flows and redundancy.

[0093] Some implementations may also consider the connectivity of individual ToRs. For example, the service level provided by a given aggregation switch or access router may vary depending on how many ToR switches are connected (indirectly or directly) to the aggregation switch or router. Again, network operators can manually examine physical and/or logical connections in the data center to determine the number of ToRs that are connected to a given aggregation switch, and can also examine the number of ToRs connected to one or more aggregation switches in the subtree rooted at an individual access router. Some implementations may also infer the ToR connectivity or “ToR count” for aggregation switches and/or access routers by analyzing traffic data in a manner similar to that described above for identifying redundancy groups.

[0094] Generally speaking, the disclosed implementations can characterize the service level of a device or collectively characterize the service level of a group of redundant devices. Filtered events can be grouped across several dimensions e.g., by individual device, redundancy group, device model, and/or device type, and metrics can be applied to measure the service levels using the grouped events. Exemplary metrics used to characterize the grouped events can include total outage time, traffic loss, and/or total tickets. The metrics can be computed using the filtered event data from one or more data centers.

[0095] In the case of total outage time, the event analysis component can determine the total outage time of an individual device in an additive fashion, e.g., summing the individual outage minutes for each event in the filtered data set. One example of a service level, availability, can be computed based on the total uptime of a particular device over a period, such as a year. Note that this is also true of redundancy groups, e.g., the availability of a redundancy group can be calculated without calculating the availability of individual group members by considering the total outage time of the redundancy group as a whole. This can also be done for device types, e.g., the average availability of access routers as a whole can be computed based on the total uptime of multiple (e.g., all) devices of a particular type. Similar processing can be performed for individual device models (e.g., a brand X model Y access router), the average availability of the model can be computed as the total outage minutes for all of the devices of that particular model divided by the total expected operational time of all of the devices of that particular model.

[0096] In the case of traffic loss, several equations can be used. The estimated average of median traffic loss per event for a device can be defined as:

$\frac{\sum _{\forall \mathrm{events}}\left(\begin{array}{c}\left(\mathrm{traffic}·{\mathrm{before}}_{\mathrm{median}}-\mathrm{traffic}·{\mathrm{after}}_{\mathrm{median}}\right)*\\ \mathrm{Failure}\mathrm{Duration}\end{array}\right)}{\mathrm{Total}\mathrm{Events}\mathrm{Contributed}\mathrm{By}\mathrm{Device}}$

[0097] Here, the equation implies that the estimated average of median traffic loss of a given device per event can be represented by the sum, over all events, of the difference in median network traffic before and after an event multiplied by the duration of the failure, divided by the total events contributed by the device to normalize the loss on a per-event basis. To obtain this value, the median traffic before and after each event can be computed to determine the median traffic loss, and then the median traffic loss can be averaged for a given event. Note that, in this context, the term “event” can refer to any individual failure episode, and can refer to a single or multiple individual device and/or link failures that collectively relate to the event.

[0098] The estimated median traffic loss for a given device per day can be defined as:

$\sum _{\forall \mathrm{events}\in d}((\left(\begin{array}{c}\mathrm{traffic}·{\mathrm{before}}_{\mathrm{median}}-\\ \mathrm{traffic}·{\mathrm{after}}_{\mathrm{median}}\end{array}\right)*\mathrm{Failure}\mathrm{Duration}$

[0099] Here, the equation implies that the loss for the device in a day is the sum, for each event associated with that device on that day, of the difference in median traffic before and after the event multiplied by the duration of the failure. Note also that traffic flow can be aggregated (e.g., summed) across links or devices in a redundant group.

[0100] For a given device model, the percentage of traffic lost by that device model can be computed as:

$\frac{\mathrm{Traffic}\mathrm{Lost}}{\mathrm{Traffic}\mathrm{Carried}}*100=\frac{\mathrm{Traffic}\mathrm{Lost}}{\mathrm{Throughput}*\mathrm{Time}}*100$

where throughput is packets per second or bytes per second and Time is the total duration over which the calculation is performed.

[0101] In the case of total tickets, the number of total tickets for a given individual device, redundancy group, device type, or device model can be computed in a relatively straightforward fashion from the filtered events. For example, each filtered event can identify a single failed device or multiple failed devices (e.g., for merged events). The number of tickets (e.g., unique tickets) for that particular device can be computed in an additive fashion. Similarly, for a redundancy group, the number of tickets identifying at least one device from the group can be computed in an additive fashion. For a device type (e.g., access router) the number of tickets identifying any access router can be computed in an additive fashion. For a device model, (e.g., brand X model Y access router), the number of tickets identifying a particular model can be computed in an additive fashion. This concept is readily extensible to other concepts related to service levels, e.g., total downtime for a platform or group of devices can be another appropriate metric.

[0102] Using the above metrics, device service levels can be characterized and the service level of an application can be computed using the service levels of the individual devices/redundancy groups in the network stamp(s) of the application. Further implementations may consider other network configuration aspects, e.g., device properties, connectivity, etc.

[0103] Device properties for a network device can reflect configuration parameters, software or firmware revisions, the particular application that is communicating through the device, etc. Some implementations can calculate individual metrics on a property-by-property basis to capture how different device properties may influence service levels. For example, the availability of access routers having a particular model with a particular software/firmware revision can be determined. As another example, the availability of aggregation switches used to route traffic from a search application can be determined, and may be different than the availability of similarly-configured aggregation switches that route traffic for a different application (e.g., cloud storage).

[0104] Some implementations may also consider device connectivity or capacity and determine the aforementioned metrics for different levels of connectivity. For example, assume up to 80 ToR switches can be connected to a single aggregation switch. Some implementations may characterize the traffic loss of an aggregation switch based on the number of connected ToRs. To the extent the ToR connectivity influences the traffic loss of the aggregation switch, such implementations may uncover this relationship. This can also be the case at other layers, e.g., the number of aggregation switches connected to a given access router can be considered as well. Also note that this processing can be performed across multiple layers, e.g., some implementations may characterize service levels of access routers based on the total number of connected ToRs in the subtrees rooted at the access routers.

[0105] Referring back to FIG. 8, the following will introduce some simple numerical examples to elaborate on the concepts expressed above. As with the previous hypotheticals, unless otherwise indicated, assume all devices shown in FIG. 8 exhibit 100% availability. Considering application 802, note that a failure at either aggregation switch 110(2) or access router 108(2) causes the entire subtree rooted at the failing device to lose connectivity. For the purpose of this hypothetical, assume the access router 108(2) has 90% availability. Thus, the availability of application 802 in this instance is computed as 90%, since the only point of failure has 90% availability.

[0106] Now, consider application 116 and again assume only the access routers have any failures and have availability of 90%, or the probability of a failure at any given time is 10%. Since access routers 108(1) are employed in a redundant group, assuming statistical independence, the probability of a co-occurrence of failures is (0.1)ⁿ, where n is the number of redundant devices in the group. In the example shown, there are two devices, so the probability of both devices failing is 0.01. Thus, deploying the access routers in a redundant pair results in 99% availability.

[0107] Given the above, one way to use ticket counts is to represent devices or device families (e.g., a particular model number) using an ordered tuple <availability, ticket count, traffic loss>. For device families, the ticket counts can be aggregated for each individual device from a given family. The tuples can be compared using lexicographic ordering e.g., if availabilities are the same or similar, then the device family with the lower ticket count is preferred because it implies that the number of impactful failures is smaller. Similarly, the traffic loss can be used for comparison—relatively small loss is preferred over device families (platforms) which cause high traffic loss during outages. Conversely, device families with high ticket counts and/or traffic loss can be considered “risky” device families. These risky families can be identified by lexicographically ordering device families based on ticket count/traffic loss and selecting the device families with high ticket counts/traffic loss. Risky device families can also be identified by applying thresholds to ticket counts/traffic loss, e.g., device families having greater than a threshold ticket frequency or greater than a threshold percentage traffic loss can be considered risky. Similar analyses can be performed using other metrics, e.g., device failure rates, etc.

[0108] The previous examples illustrate how the event analysis component can characterize the service level of an existing network configuration. The event analysis component can also estimate the service level of a proposed configuration reflecting one or more changes to the network. For example, assume a configuration change is contemplated to remove a single router from access router pair 108(1). In this case, the event analysis component could estimate the availability of application 116, after the configuration change, as 90% (e.g., n=1). Alternatively, the event analysis component can estimate the availability of application 116 if another access router were added as 99.9% (e.g., n=3). Further implementations may account for the extent to which access router failures may be correlated (e.g, simultaneous, at least partially overlapping, or in temporal succession).

[0109] Note that this analysis can also extend to different devices or data centers, e.g., assume application 802 is hosted on a single data center with 90% availability. A potential network change could be to host application 802 on 3 identical data centers, each providing 90% availability. Assuming statistical independence of the data centers, the estimated availability of application 802 would be 99.9% if this change were made. Alternatively, if the individual data centers provide different estimated availability and are assumed to be statistically independent, the individual network stamps of the application at each data center can be evaluated independently and multiplied to obtain an estimated availability. This is the case provided the individual data centers have enough capacity to handle the full application traffic load when other data centers are unavailable.

[0110] In some implementations, the event analysis component can identify various network changes that can meet a particular constraint. One type of constraint is defined by a Service Level Agreement (“SLA”). For example, the operator of the data center may be contractually obligated to provide 99.8% availability for application 116. Recall that, in the example of FIG. 8, application 116 has 99% availability at a single point of failure, the redundant pair of access routers 108(1). In this example, the event analysis component could identify hosting application 116 at an additional data center as one potential change, because two data centers with 99% individual availability would be expected to provide 99.99% availability. Alternatively, the event analysis component could identify configuring a third access router with the pair of access routers 108(1) in a redundant configuration as another potential change that would meet the SLA-required availability for application 802. This is the case since each individual access router is expected to provide 90% availability, resulting in an expected availability of 99.9% (assuming statistical independence).

[0111] FIG. 9 illustrates another GUI screenshot 900 that can be generated by the output component 512 of event analysis component 408. GUI screenshot 900 illustrates availability of application 116 in a current configuration at 99%, as well as availability of application 116 in the potential configuration with an additional access router as 99.9% and at an additional data center as 99.99%. GUI screenshot 900 also includes an SLA requirement 901, illustrated as a line reflecting the level of network availability defined by the SLA. Thus, a user viewing GUI screenshot 900 can see that, while the current configuration does not meet the SLA, the addition of a redundant access router to access router pair 108(1) will enable the network stamp of application 116 to meet the SLA, as would hosting the application at another identical data center.

[0112] Some implementations may also convey costs associated with the various potential configuration changes, e.g., adding currency, hourly, or other resource costs to GUI screenshot 900 for each potential change, e.g., on a secondary Y axis, textual representation, pie chart, etc. Some implementations may also represent the costs on a per-unit of availability basis, e.g., 1 additional “9” of availability (from 90% to 99%, 99% to 99.9%, etc.) is expected to cost a certain amount of resources. For example, FIG. 9 shows the cost in dollars for adding an additional data center is far higher than the cost to add an additional access router. In this instance, it may be appropriate to add the additional access router rather than add another data center, because both proposed configurations meet the SLA requirement and adding the access router is far cheaper.

[0113] Also note that some potential network changes may consider connectivity. For example, assume a different hypothetical where all of the devices except the aggregation switches exhibit 100% availability, and the availability of the aggregation switches varies with ToR connectivity. Specifically, consider an example where aggregation switches connected to 50 or fewer ToRs exhibit 90% availability and aggregation switches connected to 51 or more ToRs exhibit 80% availability. Now, assume that the network stamp of application 802 includes a total of 80 ToRs and two non-redundant aggregation switches, the first of which has 60 connected ToRs and the second of which has 20 connected ToRs. In this example, the event analysis component can compute estimated availability of 80% for the first aggregation switch and 90% for the second aggregation switch. Assuming statistical independence, the estimated availability for the subtree is 98% in this configuration. The event analysis component 408 can identify a potential change to move at least 10 of the connected ToRs over to the second aggregation switch, since this would not change the estimated availability of the second aggregation switch and would increase the estimated availability of the first aggregation switch to 90%, for a subtree with an estimated 99% availability. This is the case provided there remains sufficient capacity in place for any application from which the ToRs are moved.

[0114] In the hypothetical examples discussed above, statistical independence between failures in various devices was assumed to allow for relatively simple exemplary computations. In practice, some devices may exhibit some statistical correlation in their failures. For example, a pair of redundant access routers may tend to fail together due to problems common to both of the access routers. For example, both access routers may have a bug in the software/firmware, power outages or spikes could cause both routers to fail, overload conditions could affect both routers concurrently, etc. However, note that highly correlated failures can be undesirable, particularly for redundant devices. This is because, as discussed above, when redundant devices in a group fail together, they are not available to take over functioning for each other.

[0115] In view of the above, some implementations may identify certain groups of risky devices in a given network configuration. FIG. 10 shows a method 1000. For example, method 1000 can be performed by event analysis component 408 to characterize groups of devices as “risky,” meaning the devices are relatively likely to fail together rather than individually.

[0116] At block 1002, the method can obtain a set of events logged at a data center. Block 1002 can be similar to block 702 of method 700.

[0117] At block 1004, the method can method can filter the events using one or more criteria. Block 1004 can be similar to block 704 of method 700.

[0118] At block 1006, the method can characterize service levels of one or more devices using the filtered sub-set of the events. For example, the method can determine the individual availability of multiple access routers in a redundancy group at the L3 aggregation layer, or multiple aggregation switches at the L2 aggregation layer.

[0119] At block 1008, the method can determine correlations between the service levels of the individual devices. For example, some implementations may compute the correlation (e.g., Pearson correlation) between tickets, outage minutes, or traffic loss for devices within an individual redundancy group. Some implementations may also compute the correlation between tickets, outage minutes, or traffic loss of connected devices at different layers, e.g., between an individual aggregation switch and an individual access router.

[0120] At block 1010, the method can identify risky devices based on the correlations. For example, the correlations can be compared to a threshold, and devices having a correlation exceeding the threshold can be identified as risky because these devices may tend to fail together (e.g., failures with a temporal relationship such as overlapping failures or tending to fail in succession). As one example, access routers or aggregation switches in a redundancy group that tend to fail together can be risky because the redundancy is less effective when the devices tend to fail together. As another example, failures of a device at one layer can tend to cause failures of devices at other layers, e.g., failed ToRs can tend to bring down upstream aggregation switches and this can be apparent from the correlations. Note also that individual devices that tend to fail frequently can also be identified at block 1010 (e.g., devices with a high number of failures).

[0121] The service levels used for method 1000 can include the various service levels mentioned above, e.g., total outage time, total tickets, traffic loss, etc. Note, however, that other metrics may be suitable. Furthermore, while the following implementations discuss Pearson correlation as a suitable measure of correlation, other correlation measures can also be used such as Spearman's rank correlation coefficient and/or Kendall tau rank correlation coefficient.

[0122] Considering total outage time, one way to correlate outage time between two devices is as follows. First, the total downtime of a device A and the total downtime of a device B are determined from filtered events, as discussed above. Next, the filtered events are also used to determine individual events where both device A and B were down together, or at least partially overlapping in terms of their time window of being unavailable. If there is a strong negative correlation between failures of devices A and B (e.g., Pearson coefficient close to −1), then the overlapping failures will tend to be relatively minimal relative to the individual failure rates of the devices—in other words, the devices are less likely to fail together than would be the case if there were no correlation. If there is minimal or no correlation (e.g., Pearson coefficient of approximately 0), then the devices tend to fail independently of one another, e.g., the failure of one device has little or no apparent impact on whether the other device fails. If there is a strong correlation (e.g., Pearson coefficient close to 1), there is a strong correlation and the devices are more likely to fail together than would be the case if the failures were independent.

[0123] This last case, relatively high correlation, can be problematic for devices in a redundant configuration for reasons already mentioned. Thus, in some implementations, risky devices can be devices deployed in a redundant configuration that have a correlation exceeding a certain threshold, e.g., 0.7. Similar processing can be employed with respect to network tickets by determining the Pearson coefficient for support tickets, e.g., determining the total number of tickets for each individual device and the intersection of these tickets that relate to both devices. Assuming an equivalent number of tickets, smaller intersections imply lower correlations and larger intersections imply higher correlations. Correlations can also be determined for losses of network traffic by individual devices, e.g., if traffic loss by one device in a redundant pair tends to be highly correlated to traffic loss by another device in the redundant pair, the pair can be flagged as a risky device pair.

[0124] FIG. 11 illustrates another GUI screenshot 1100 that can be generated by the output component 512 of event analysis component 408. GUI screenshot 1100 shows correlations for three redundant access router pairs (“AR pairs”). GUI screenshot 1100 also shows a correlation threshold 1101, which is shown as a line representing the threshold for characterizing an individual device group as “risky.” Thus, GUI screenshot 1100 shows that redundant AR pair 3 is risky because the correlation exceeds the threshold. In some implementations, GUI screenshot 1100 may allow user inputs to move the correlation threshold 1001 up or down and recharacterize device groups accordingly. For example, if the user moved the threshold down to 0.53, then redundant AR pair 2 would also be characterized as a risky AR pair.

[0125] Note that some implementations may perform processing similar to that discussed above with respect to method 1000 to determine risky device properties. For example, consider a data center with many physically identical network devices, a first group of which have a first software/firmware revision, Revision A and a second group of which have a second software/firmware revision, Revision B. One device property for these devices may reflect the current revision. If Revision A is highly correlated (e.g., using one or more of the correlation measures mentioned above) to tickets, outages, or traffic loss, then this property can be flagged as a risky property. In further implementations, the event analysis component may evaluate the data center topology to identify those devices having the risky property (e.g., Revision A). The event analysis component may also estimate the change in device availability if the Revision A devices were upgraded to revision B. Based on the estimated individual device availability, the event analysis component can also estimate the change in application availability for applications having network stamps that include one or more Revision A devices.

[0126] The order in which the disclosed methods are described is not intended to be construed as a limitation, and any number of the described blocks can be combined in any order to implement the method, or an alternate method. Furthermore, the methods can be implemented in any suitable hardware, software, firmware, or combination thereof, such that a computing device can implement the method. In one case, the methods are stored on one or more computer-readable storage media as a set of instructions such that execution by a processor of a computing device causes the computing device to perform the method.

[0127] Although techniques, methods, devices, systems, etc., pertaining to characterizing service levels are described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as exemplary forms of implementing the claimed methods, devices, systems, etc.