Patent Publication Number: US-11037033-B2

Title: Multivariate clustering-based anomaly detection

Description:
BACKGROUND 
     The disclosure generally relates to the field of data processing, and more particularly to software development, installation, and management. 
     Generally, a distributed application is an application that includes software components that are distributed across multiple networked host machines which may be physical machines or virtual machines. The distributed application presents an interface(s) to a client for requesting a transaction to be performed. Performing the transaction includes performing multiple operations or tasks, or “end-to-end” tasks of the transaction. Each component of the distributed software application handles a different subset of those tasks. This application architecture allows for a more flexible and scalable application compared with a monolithic application. 
     Large-scale distributed applications have a variety of components including web services and/or microservices. A distributed tracing tool can be used to trace an execution path through these various components. As the software components are executed (e.g., remote procedure calls, remote invocation calls, application programming interface (API) function invocations, etc.), identification of the component is recorded, and the sequence of calls/invocations are correlated to present the execution path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the disclosure may be better understood by referencing the accompanying drawings. 
         FIG. 1  is a diagram of a topology-based multi-variate anomaly detection service that intelligently selects features by transaction type to detect anomalies. 
         FIGS. 2-3  illustrate a flowchart of example operations for establishing scanners to detect known anomalies by transaction type in a distributed application. 
         FIG. 4  is a flowchart of example operations for scanning time-series measurements of instances of blame metrics of a specific application component(s). 
         FIG. 5  is a flowchart of example operations for establishing scanners to detect unknown anomalies by transaction type in a distributed application. 
         FIG. 6  is a flowchart of example operations for scanning time-series measurements of instances of metrics of a specific application component(s). 
         FIG. 7  is a flowchart of example operations for detecting known and unknown anomalies in a distributed application based on multivariate clustering analysis. 
         FIG. 8  is a visualization of cluster detection for points from a distributed application. 
         FIG. 9  illustrates a flowchart of example operations to train and label clusters for an anomaly detector. 
         FIG. 10  depicts an example computer system with a multivariate clustering-based anomaly detector. 
     
    
    
     DESCRIPTION 
     The description that follows includes example systems, methods, techniques, and program flows that embody the disclosure. However, it is understood that this disclosure may be practiced without these specific details. For instance, the description refers to a service (e.g., APM manager and anomaly detection service), but the described functionality can be embodied as tools or applications that are not necessarily services. In other instances, well-known instruction instances, protocols, structures and techniques have not been shown in detail in order not to obfuscate the description. 
     INTRODUCTION 
     A large-scale distributed application can include numerous software components distributed across an infrastructure comprising numerous machines (e.g., servers, storage arrays, routers, etc.). The distributed application provides different transactions to clients (e.g., customer check-in, purchasing, etc.) that variously traverse the application components and the infrastructure layer (e.g., routers, storage arrays, etc.) that supports them. Monitoring agents are deployed throughout the components of the layers of a distributed application (e.g., an infrastructure layer and an application layer). The monitoring agents determine measurements for application related metrics and report them to an application performance management manager (“APM manager”). An “application related metric” refers to a measurable attribute of a component(s) of an application, examples of which include available memory, number of active sessions, throughput, latency, average response time, responses per interval, stall counts, and errors per interval. The APM manager detects events that likely impact application performance and/or correspond to the application operating in an undesirable way. An event that impacts application performance is considered an anomaly or indication of an anomaly because it corresponds to behavior that is anomalous with respect to canonical application behavior. An anomaly event may be directly based on an application related metric or derived from one or more application related metrics. An anomaly event can be generated from the distributed application (e.g., component restart event) or can be generated based on a measurement(s) or value computed from measurements (e.g., an average of measurements). For instance, an anomaly event may indicate that average response time of a component or for a transaction exceeds a defined threshold. This comparison of a measurement against a threshold is typically how anomalies are detected. The APM manager analyzes those events to diagnose the cause of the events and determine a corrective action. 
     Many anomalies correlate to multiple application related metrics instead of a single application related metric. Measurements of a set of application related metrics (hereinafter “metrics”) over time indicate a behavior of the set of metrics as represented by a trend among the multiple metrics (“pattern”). However, reading and analyzing (collectively “scanning”) all measurements of all metrics monitored is at least computationally challenging. Monitoring agents of a distributed application may be monitoring thousands of instances of metrics (e.g.,  30  categories of metrics across hundreds of components) resulting in the generation of half a million measurements per hour, assuming a sampling rate of 60 seconds. In addition to the measurements collected at the sampling rate, other measurements are passively collected (e.g., injected measurement logic). Searching a 1000-dimensional space for a pattern is not only computationally challenging but such efforts would be counterproductive by producing effectively useless results either due to the volume of patterns detected or the amount of noise in the detected patterns. 
     Overview 
     A multivariate clustering-based anomaly detection service (“anomaly detector”) can generate an event for consumption by the APM manager that indicates detection of an anomaly based on multivariate clustering analysis after topology-based feature selection. The anomaly detector reads in time-series data (i.e., measurements of application related metrics) collected and/or generated from monitoring agents. The anomaly detector accumulates the time-series data across a series of discrete time instants to form a multivariate time-series data slice or multivariate data slice. The anomaly detector then performs multivariate clustering analysis with the multivariate data slice. The anomaly detector determines whether a multivariate data slice is within a cluster of multivariate data slices. If the multivariate data slice is within the cluster and the cluster is a known anomaly cluster (i.e., a cluster of multivariate data slices correlated to a known anomaly), then the anomaly detector generates an anomaly detection event indicating detection of the known (i.e., named) anomaly. The anomaly detector can also determine that a multivariate data slice is within an unknown cluster (i.e., a cluster of multivariate data slices correlated to neither canonical behavior nor a known anomaly) and generate an event indicating detection of an unknown anomaly. 
     Example Illustrations of Topology-Based Feature Selection 
       FIG. 1  is a diagram of a topology-based multi-variate anomaly detection service that intelligently selects features by transaction type to detect anomalies.  FIG. 1  depicts monitoring agents  107   a - 107   n  deployed across components of a distributed application  106 . The monitoring agents  107   a - 107   n  communicate with an APM manager  102 . The APM manager  102  creates and maintains an application topology map  105  for the distributed application  106 . The APM manager  102  also creates and maintains traces or execution paths  103 . Since the distributed application  106  is presumed to provide multiple types of transactions and each instance of a transaction type likely does not traverse a same execution path,  FIG. 1  illustrates multiple execution paths for the presumed multiple transaction types.  FIG. 1  also depicts an example architecture of a topology-based multi-variate anomaly detection service  101 . The topology-based multi-variate anomaly detection service  101  scans for known anomalies based on anomaly models loaded into or accessible by the topology-based multi-variate anomaly detection service  101 . 
     The anomaly models include a model  113  for an anomaly  1  and a model  115  for an anomaly  2 . The known anomalies are typically named for human comprehension to facilitate efficient triage/troubleshooting. For instance, anomaly  1  may be “memory leak” and anomaly  2  may be “death by a thousand cuts.” The models can be defined based on expert knowledge that identifies behavior of a set of metrics that correlate to a performance issue. An anomaly model describes this behavior or pattern formed by measurements of a specified set of metrics over time that correlates to the anomaly (“anomaly blame metrics”) represented by the model. The anomaly blame metrics may be for a single component (“intra-component”) or among multiple components (“cross-component”). An anomaly model for APM specifies a component type(s) (e.g., virtual machine, router, database) and the anomaly blame metrics of the specified component type(s). The anomaly model can describe the behavior of the anomaly blame metrics with different techniques. For instance, the anomaly model can “describe the behavior” with a covariance matrix generated from multivariate analysis of covariance (MANCOVA) from previously evaluated measurements correlated with an anomaly (e.g., lab measurements and/or actual deployed product measurements). The covariance indicated by the covariance matrix represents the pattern of the anomaly blame metrics. As another example, an APM anomaly model can describe the behavior of the set of metrics with a set of conditions to evaluate the pattern formed by measurements of the blame metrics. The conditions can be based on directions of measurements, rate of change of measurements of a metric with respect to one or more other metric measurements, frequency of directional changes across metrics, and changes in measurements with respect to external factors (e.g., time of day). As another example, an anomaly model can include a set of functions that represent a pattern formed by measurements of blame metrics. Examples of the set of functions include an average, summation, and decompositions (e.g., decompose into a trend component, cyclical component, seasonal component, a noise component). 
       FIG. 1  includes stages A-E 2  as example stages of operation to aid in illustrating operation of the topology-based multi-variate anomaly detection service  101 . Each stage can correspond to one or multiple operations. The described example stages of operations should not be used to limit scope of the claims. 
     During a stage A, the monitoring agents  107   a - 107   n  communicate a vast number of metric measurements for the distributed application  106  to the APM manager. As previously indicated, the measurements can span a variety of types of metrics and different layers of the distributed application. These measurements are written into a measurement repository  104  of the APM manager  102 . The monitoring agents  107   a - 107   n  and/or the APM manager  102  writes the measurements as time-series data (i.e., into data structures that reflect that collection of measurements over time). Measurements can be a transaction, underlying hardware components, individual software components, etc. This illustration focuses on the measurements per component. The measurement repository  104  is illustrated to represent organization of at least some measurements by component. Regardless of the specific implementation of the measurement repository  104 , measurements can be accessed by component identifier. A component identifier may encode a host identifier and a specific component identifier (e.g., HOST1_VM). 
     When the topology-based multi-variate anomaly detection service  101  starts, the service  101  queries the APM manager  102  for the execution paths  103  of the distributed application  106 . Before querying for the execution paths, the service  101  may query the APM manager  102  for the transaction types provided by the distributed application  106 , if not already known (e.g., programmed/configured into the service  101 ). With the simple example of two transaction types, the service  101  at stage B 1  determines an execution path  103   a  for a transaction type A and at stage B 2  determines an execution path  103   b  for a transaction type B. Based on the execution paths, the service  101  instantiates scanners to scan the components of the execution paths for anomalies. The service  101  instantiates scanners  109   a  for the transaction type A and scanners  109   b  for the transaction type B. In this example architecture, the scanners  109   a - 109   b  are programmed to read the time-series measurements from the measurement repository  104  to form multivariate data slices and analyze the multivariate data slices against the anomaly models  113 ,  115 . 
     The service  101  determines components and metric instances in the execution paths relevant to each of the anomaly models, and then instantiates the scanners accordingly. For this illustration, anomaly  1  model  113  describes behavior of blame metrics of a virtual machine. The anomaly  2  model  115  describes the blame metrics of a database. The entries  121  (e.g., records, subtree nodes, etc.) of the measurement repository  104  include time-series measurements of metrics collected for a database instance of the distributed application  106  in the execution path  103   a . The entries  123  include time-series measurements of metrics collected for a host in the execution path  103   a  and for a virtual machine on the host. The entries  123  include time-series measurements of metrics collected for a host in the execution path  103   b  and for a virtual machine on the host. The service  101  determines that the anomaly  1  model  113  indicates blame metrics of a virtual machine for the represented anomaly, and then identifies an instance of a virtual machine in the execution path  103   a . The service  101  instantiates one of the scanners  109   a  to read the entries  123  that correspond to the blame metrics indicated in the anomaly  1  model  113  at stage C 1  and analyze the measurements read from entries  123  at stage D 1  to detect whether the measurements form a pattern indicated in the model  113 . The service  101  also identifies the instance of the virtual machine in the execution path  103   b  as relevant to the model  113 , and instantiates one of the scanners  109   b  to read the entries  125  that correspond to the blame metrics of the model  113  at stage C 2 . At stage D 2 , the instantiated scanner  109   b  determines whether measurements read from the entries  125  form the pattern indicated in the model  113 . For the anomaly  2  model  115 , the service  101  determines that that the model  115  indicates a database as a relevant type of component. The service  101  determines that the execution path  103   b  does not include a database instance and does not instantiate a corresponding scanner. The service  101  determines that the execution path  103   a  includes a database instance, which is a relevant component type for the model  115 . The service  101  determines the blame metrics of anomaly  2  as indicated in the model  115  and instantiates one of the scanners  109   a  to read the blame metric measurements from the entries  121  for the database instance in the execution path  103   a  at stage C 1 . The service  101  also instantiates the scanner to determine whether measurements read from the entries  121  form a pattern indicated in the model  115  for anomaly  2  at stage D 1 . 
     If one of the scanners  109   a ,  109   b  detects a pattern corresponding to either of the anomalies represented by the models  113 ,  115 , then the scanner generates an event for consumption by the APM manager  102 . At stage E 1 , one of the scanners  109   a  determines that measurements read from the measurement repository  104  form a pattern indicated in one of the models  113 ,  115  and generate a corresponding event. The event indicates the anomaly name and corresponding component(s) of the distributed application  106 . The event can also indicate the transaction type, and other information that can be used for triage of the named anomaly. At stage E 2 , the scanner  109   b  detects a pattern in measurements read from the entries  125  that satisfies the pattern indicated in the model  115 . Due to the dynamic nature of applications, the service  101  intermittently or periodically refreshes the execution paths that inform the scanning. Over time, execution paths can change and different transaction types can become active/dormant. For example, certain types of transactions may not be performed during business hours. Thus, an APM manager may not have an execution path for an inactive or dormant transaction type. 
     The implementation illustrated in  FIG. 1  is an example illustration. Embodiments can instantiate scanners differently according to available resources, policies, etc. For instance, a topology-based multi-variate anomaly detection service can divide the labor of identifying and reading blame metrics indicated in an anomaly model for relevant components from analyzing the measurements to detect an anomaly pattern. The topology-based multi-variate anomaly detection service can instantiate an analyzer per anomaly model and instantiate a reader per relevant component instance of available/active execution paths per anomaly model. For example, the detection service instantiates 4 readers when x execution paths include 4 different instances of a component relevant to an anomaly model. These 4 readers can read time-series measurements into data structures for analysis (e.g., matrices) and insert them into an input queue for the analyzer instantiated for the anomaly model. Embodiments can also program scanners to form multivariate data slices and invoke analyzer program code with arguments that include an anomaly model identifier and the multivariate data slice. 
       FIGS. 2-3  illustrate a flowchart of example operations for establishing scanners to detect known anomalies by transaction type in a distributed application. The description of  FIGS. 2-3  refers to an anomaly detector as performing the operations. The anomaly detector for these example operations instantiates a scanner for each relevant component of each known anomaly model loaded into the anomaly detector for each transaction type execution path. The example operations of  FIGS. 2-3  distinguish between an intra-component anomaly model and a cross-component anomaly model. 
     The anomaly detector initially determines transaction types of a distributed application associated with the anomaly detector ( 202 ). The anomaly detector may query an APM manager to determine transaction types if not already input to the anomaly detector. The anomaly detector determines the provided types of transactions based on an assumption that each transaction type will have a different execution path and/or that a detected anomaly should be associated with a transaction type. 
     For each determined transaction type ( 204 ), the anomaly detector gathers information to instantiate appropriate scanners for each known anomaly model relevant to the transaction type. The description refers to a transaction type in a current iteration as a current transaction type. The anomaly detector retrieves an aggregate execution path of the current transaction type ( 206 ). Each instance of the current transaction type can have some variation in execution path. Therefore, the execution paths of multiple instances of a same transaction type can be aggregated into a single execution path. The anomaly detector then determines application components on the aggregate execution path for the current transaction type ( 208 ). Each node in the execution path corresponds to a component of the distributed application and each component will be identified (e.g., network address, host name concatenated with component name, etc.). In addition to an identifier, the node in the execution path either indicates a type of the component or the component identifier can be used to determine component type. 
     For each anomaly model based on intra-component metric behavior ( 210 ), the anomaly detector determines relevant components to scan. The description refers to an intra-component anomaly model of a current iteration as a current intra-component anomaly model. The anomaly detector identifies each component in the execution path of the current transaction type that is relevant to the current intra-component anomaly model ( 212 ). Each component in the current transaction type execution path of a same type as that indicated in the current intra-component anomaly model is determined to be relevant. For each relevant component in the current transaction type execution path ( 214 ), the anomaly detector instantiates a scanner configured to scan the instances of the blame metrics of the relevant application component ( 216 ). The anomaly detector can invoke a subroutine that instantiates a process/thread to read time-series measurements of blame metrics identified in the current intra-component anomaly model. To “configure” the scanner, the anomaly detector can invoke the subroutine with arguments that include indications of the blame metrics and an identifier of the relevant component identifier. The scanner can be programmed with the protocol to access an APM measurement repository and use component identifier and indications of the blame metrics to access the measurements for detection of the known anomaly represented by the current intra-component anomaly model. The anomaly detector can also “configure” the analyzing aspect of the scanner by passing as arguments the anomaly model and a subroutine identifier for the particular analysis to be performed, if any. In some cases, the anomaly model embodies logic and/or conditions that collectively describe a pattern of blame metric measurements that correlate to the known anomaly. If an anomaly event should identify a transaction type, then an indication of the transaction type is associated with the scanner for propagation into a generated anomaly detection event. After instantiation of the configured scanner, the anomaly detector determines whether there is an additional application component in the aggregate execution path of the current transaction type that is relevant to the current intra-component anomaly model ( 218 ). If so, then the anomaly detector proceeds to instantiating the scanner for that relevant component. Otherwise, the anomaly detector determines whether there is an additional intra-component anomaly model to process ( 220 ). If there is not an additional intra-component anomaly model to process, the anomaly detector proceeds to any installed anomaly models based on cross-component metric behavior ( FIG. 3 ). After processing cross-component anomaly models for the current transaction type, the anomaly detector proceeds to the next transaction type, if any ( 224 ). 
       FIG. 3  continues from  FIG. 2  for any installed cross-component anomaly models. The operations in  FIG. 3  are similar to those for intra-component anomaly models ( 210 ,  212 ,  214 ,  216 ,  220 ). For each anomaly model based on cross-component metric behavior ( 301 ), the anomaly detector determines relevant component sets to scan. The anomaly detector determines whether there is a set of components in the aggregate execution path of the current transaction type that is relevant to the cross-component anomaly model ( 303 ). In addition to relevancy based on component types, a cross-component anomaly model can indicate a degree of adjacency or connection for blame metrics among a set of components. A pattern of measurements of blame metrics across components in a cross-component anomaly model may be limited to occurring when those relevant components are adjacent to each other, for instance. If the execution path of the current transaction type includes the relevant component set ( 214 ), then the anomaly detector instantiates a scanner configured to scan the instances of the blame metrics of the relevant application components ( 305 ). After instantiation of the configured scanner, the anomaly detector determines whether there is an additional cross-component anomaly model to process ( 307 ). If there is not an additional cross-component anomaly model to process, the anomaly detector proceeds to a next transaction type ( 224 ). 
       FIG. 4  is a flowchart of example operations for scanning time-series measurements of instances of blame metrics of a specific application component(s). The example operations of  FIG. 4  represent the operations performed by instantiated scanners. The description of  FIG. 4  refers to a scanner as performing the example operations. The example operations presume the scanner has been configured or instantiated with an identifier of an application component or identifiers of a set of application components and indications of the corresponding blame metrics. The example operations in  FIG. 4  are written to apply to either blame metrics of an intra-component anomaly model or a cross-component anomaly model. 
     A scanner reads in time-series measurements of the specified blame metrics of the identified application component(s) to form a multivariate data slice according to a slice width defined for the pattern described in the known anomaly model for which the scanner was instantiated ( 402 ). The slice width defines a number of observations or time instants of the blame metrics to collect for analysis. The scanner can buffer blame metrics measurements until the slice width is satisfied and then populate a P×T matrix (P being the number of blame metrics and T being the number of time instants) with the buffered measurements or populate the matrix with the measurements as read in from the measurement repository ( 404 ). The scanner then analyzes the matrix based on the pattern indicated in the known anomaly model ( 406 ). The analysis depends upon how the pattern is indicated in the known anomaly model. If the pattern is described with logic that evaluates conditions (e.g., m 1  and m 2  increase at rate beyond rate change threshold while m 3  decreases), then the analysis determines attributes of the blame metric measurements (rates of change, directional changes, flapping, etc.) and compares those attributes against the pattern attributes indicated in the logic/conditions of the known anomaly model. For a logic based model, the anomaly detector may normalize some or all of the blame metric measurements prior to evaluation since magnitude of those measurements may not be relevant to the analysis. If the pattern is indicated in the known anomaly model as a set of functions, then the scanner determines whether the measurements in the matrix fit the set of functions within a specified margin of variance. 
     Based on the analysis, the scanner determines whether an anomaly pattern has been detected ( 408 ). If so, then the scanner generates an event indicating detection of the named anomaly ( 410 ). As previously mentioned, the event can also indicate the component(s) and the transaction type. If an anomaly pattern was not detected, then the scanner discards the matrix ( 412 ) and proceeds to a next data slice. Embodiments may analyze a sliding window of blame metrics measurements instead of discrete slices. In that case, the scanner continuously updates the matrix or other data structure used to store the blame metrics measurements to insert the blame metrics measurements of a newest time instant and removes those of the oldest time instant. 
     The preceding example illustrations have scanned for named anomalies represented by known anomaly models. Embodiments can also scan for unknown/unnamed anomalies by looking for patterns that vary beyond an acceptable margin from a canonical behavior of performance metrics.  FIGS. 5-6  present flowcharts of example operations for scanning for unknown anomalies. 
       FIG. 5  is a flowchart of example operations for establishing scanners to detect unknown anomalies by transaction type in a distributed application. Although there are some similar operations between  FIG. 5  and  FIG. 2 , the example operations in  FIG. 5  are analyzing specified metric measurements to detect a pattern(s) of behavior that deviates from a canonical behavior that has been determined for a distributed application. 
     The anomaly detector determines transaction types of a distributed application associated with the anomaly detector ( 502 ). The anomaly detector may query an APM manager to determine transaction types if not already input to the anomaly detector. Since execution paths are dynamic, the anomaly detector can subscribe to receive changes or updated execution paths. Or the anomaly detector can periodically request active execution paths (i.e., execution paths of transactions that have occurred in a recent time window). 
     For each determined transaction type ( 504 ), the anomaly detector gathers information to instantiate appropriate scanners to determine deviation from canonical behavior as represented by one or more sets of metrics. The description refers to a transaction type in a current iteration as a current transaction type. The anomaly detector retrieves an aggregate execution path of the current transaction type ( 506 ). As previously mentioned, each instance of the current transaction type can have some variation in execution path. Therefore, the execution paths of multiple instances of a same transaction type can be aggregated into a single execution path. The anomaly detector then determines application components on the aggregate execution path for the current transaction type ( 508 ). The execution path includes and/or references information that identifies each component and at least indicates component type. 
     For each canonical model ( 510 ) for the transaction type, the anomaly detector determines relevant components to scan. Although  FIG. 2  referred to intra-component anomaly models and cross-component anomaly models, each canonical model referred to in  FIG. 5  can be based on behavior of multiple metrics of an individual component or across components. A canonical model can be per component or per transaction type. For instance, a canonical model can describe a pattern of metrics for a component for canonical behavior regardless of transaction type. A canonical model can describe a pattern of metrics for one or multiple components for canonical behavior of the distributed application for a particular transaction type or group of transaction types. The anomaly detector identifies each component in the execution path of the current transaction type that is relevant to the current canonical model ( 512 ). Each component in the current transaction type execution path of a same type as that indicated in the current canonical model is determined to be relevant. 
     For each relevant component in the current transaction type execution path ( 514 ), the anomaly detector instantiates a scanner configured to scan the instances of the metrics of the relevant application component ( 516 ). The anomaly detector can invoke a subroutine that instantiates a process/thread to read time-series measurements of metrics identified in the current canonical model. The anomaly detector can configure the scanner as previously described in  FIG. 2 . After instantiation of the configured scanner, the anomaly detector determines whether there is an additional application component in the aggregate execution path of the current transaction type that is relevant to the current canonical model ( 518 ). If so, then the anomaly detector proceeds to instantiating the scanner for that relevant component. Otherwise, the anomaly detector determines whether there is an additional canonical model to process ( 520 ). If there is not an additional canonical model to process, the anomaly detector proceeds to the next transaction type, if any ( 524 ). 
       FIG. 6  is a flowchart of example operations for scanning time-series measurements of instances of metrics of a specific application component(s). The example operations of  FIG. 6  represent the operations performed by a scanner instantiated to determine deviation from a canonical model. The description of  FIG. 6  refers to a scanner as performing the example operations. The example operations presume the scanner has been configured or instantiated with an identifier of an application component or identifiers of a set of application components and indications of the corresponding metrics specified in the canonical model(s) for the application components. 
     A scanner reads in time-series measurements of the specified metrics of the identified application component(s) at a slice width defined for the pattern described in the canonical model for which the scanner was instantiated ( 602 ). The scanner can populate a P×T matrix according to various techniques, such as those described with reference to  FIG. 4  ( 604 ). The scanner then analyzes the matrix based on the pattern indicated in the canonical model ( 606 ). The analysis includes a pattern analysis that depends upon how the pattern is indicated in the canonical model. In contrast to  FIG. 2 , the scanner is analyzing to determine whether the slice of measurements exhibits behavior that deviates from behavior described in the canonical model. As with an anomaly model, the canonical model can describe canonical behavior differently. In one instance, a canonical model can describe canonical behavior with a set of criteria/conditions that are logically evaluated to determine deviation of measurements in a slice from canonical behavior. A canonical model can describe canonical behavior with a pattern correlated with canonical behavior. The pattern can be represented with a set of functions, values generated from MANCOVA, etc. The pattern analysis of the matrix can include determining whether the slice measurements fit, within an acceptable margin, the set of functions; generating covariance analysis values and comparing against covariance analysis values of the canonical model; etc. 
     Based on the analysis, the scanner determines whether the slice measurements exhibit metric behavior that deviates from the canonical behavior expressed in the canonical model ( 608 ). If so, then the scanner generates an event indicating detection of an unknown or unnamed anomaly ( 610 ). As previously mentioned, the event can also indicate the component(s) and the transaction type. If an anomaly was not detected, then the scanner discards the matrix ( 612 ) and proceeds to a next data slice. Similar to the scanning based on anomaly models, embodiments may analyze a sliding window of metrics measurements instead of discrete slices. 
     Since the space of metrics that can be chosen for a canonical model is substantially larger than those identified for a named anomaly, the metrics chosen for a canonical model may be arbitrary to an extent (e.g., certain metrics may never express a behavior in aggregate that correlates to a meaningful event). The metrics chosen for a canonical model can be the top x metrics that most commonly occur in anomaly models. The metrics chosen for a canonical model may be those that are not in anomaly models for which scanners have been instantiated. A canonical model generator can be programmed that periodically rotates through different sets of metrics and generates a corresponding canonical model. 
       FIG. 6  presumes a scanner searching for an unknown anomaly based on a canonical model. An anomaly detector likely compares results of analyzing multivariate data slices against the known anomaly models and the canonical model. If the pattern analysis indicates that a multivariate data slice does not exhibit behavior represented by the canonical model and none of the known anomaly models, then the anomaly detector will indicate that an unknown anomaly has been detected. With respect to  FIG. 6 , embodiments may not perform the operation represented in block  610 . Instead, the anomaly detector would generate an indication that the multivariate data slice exhibits behavior that deviates from the canonical model. If pattern analysis against the known anomaly model(s) does not generate a known/named anomaly event, then the anomaly detector would generate the unknown anomaly event. 
     In the above example illustrations, models are defined based on knowledge of domain experts. These models can be revised or updated based on machine learning techniques. Models can be revised with supervised machine learning techniques that use a previously observed dataset(s), generated from a lab and/or from deployments, to revise anomaly and/or canonical models. For instance, normalization functions can be modified based on supervised machine learning to adapt to measurements actually observed in a deployment. The machine learning technique utilized can also vary based on model type (e.g., logic based model that normalizes measurements versus a function based model that uses raw measurements). In addition, while a margin/threshold of variance can be a predefined amount (e.g., percentage) in general, per software component type, per hardware component type, etc., it can also be established or revised with a machine learning technique. A model, whether expressing a pattern as conditions and/or functions, can be trained with supervised machine learning that uses test data to establish an acceptable margin of variance. This margin of variance can be further refined/tailored by training the model with a dataset of a deployed, distributed application. Thus, the margin of variance can be static or dynamic. 
     Example Illustrations of Multivariate Clustering to Detect Known or Unknown Anomalies 
     While anomalies can be detected with pattern detection based on models as described above, multivariate clustering analysis can be employed to detect known and unknown anomalies. An anomaly detector (or other program or service) can establish a cluster(s) for canonical behavior(s) and a cluster(s) for one or more named anomalies. The anomaly detector can be deployed with clusters established based on training datasets that conform to defined models (e.g., laboratory datasets generated based on defined models). The clusters can adapt to deployment specific time-series data with or without knowledge expertise to validate cluster assignments of multivariate data slices. Embodiments can deploy the anomaly detector to initially detect anomalies based on the previously described pattern detection and use the results of that pattern detection to establish one or more known anomaly clusters and one or more canonical clusters. In addition, a tighter margin of variance can be defined for selecting multivariate data slices to establish clusters. The first centroid of each cluster can be based on the first multivariate data slices selected by the anomaly detector for cluster training, or a domain expert can select/define multivariate data slices to calculate centroids for known anomaly clusters and a canonical cluster(s). 
       FIG. 7  is a flowchart of example operations for detecting known and unknown anomalies in a distributed application based on multivariate clustering analysis. The description of  FIG. 7  refers to a scanner as performing the example operations. The description of  FIG. 7  also refers to training or updating cluster data based on pattern analysis. However, alternative training or updating methods can be applied, as described further below with reference to  FIG. 9 . 
     After forming in a current multivariate data slice, the anomaly detector transforms the multivariate data slice into a current reduced representation of the multivariate data slice (hereinafter referred to as a “point”) for cluster analysis ( 708 ). The scanner can transform the multivariate data slice using a dimension-reducing method such as principal component analysis (PCA). In PCA, the scanner generates a covariance matrix of the multivariate data slice and determines the eigenvectors of the covariance matrix with their corresponding eigenvalue. The scanner can use the eigenvector with the greatest corresponding eigenvalue (i.e., the principal component) as the point. In addition, the scanner can combine a predetermined number of eigenvectors with the greatest eigenvalues into a combined vector and use the combined vector as the point. Embodiments can generate a reduced representation of a multivariate data slice with multiple dimension reducing operations. For instance, an anomaly detector can rearrange the elements of a multivariate data slice (e.g., by concatenating all the rows of the multivariate data slice into a single vector) and then performing PCA on the rearranged multivariate data slice to generate the point. Alternatively, the scanner can transform the multivariate data slice using singular-value decomposition and use either a left-singular vector or a right-singular vector as the point. 
     For this example illustration, a cluster(s) has previously been established for canonical behavior, and clusters have been established for named anomalies. These clusters have been established for the feature set (i.e., metrics) for which the scanner has been instantiated. The anomaly detector likely has a scanner for different feature sets. Thus, other canonical and named anomaly clusters will have been established for the other feature sets. For each cluster stored or accessible by the scanner ( 720 ), the scanner will determine whether the current point should be assigned to the cluster based on distance. The scanner determines a distance between the current point and the cluster ( 728 ). The distance is equal to a Euclidean distance between the current point and a consistent position corresponding to the cluster such as the cluster centroid, the nearest point in the cluster, or a nearest topological boundary of the cluster. For example, the scanner can set the distances to be equal to the Euclidean distances between the current point and each of the cluster centroids. After determining a distance between a cluster and the current point, the scanner determines if there are additional cluster distances to determine ( 736 ). If there is an additional cluster distance to determine, the scanner will determine the additional cluster distance. Otherwise, the scanner determines if the nearest cluster is within a threshold distance ( 740 ). 
     The threshold distance can be defined based on the distance between a point in the nearest cluster and the nearest cluster centroid. In some definitions, the threshold distance can change depending on which cluster is the cluster nearest to the current point. For example, if the current point is closest to a first cluster C 1  and the greatest distance between a point in the first cluster C 1  and the centroid of C 1  is the normalized value 0.15, the threshold distance can be set to the intra-cluster distance 0.15. A distance threshold can instead be defined as a ratio of a distance from the centroid of C 1  to the furthest distance from the centroid of C 1 . For example, the threshold distance can be set to be 50% greater than the intra-cluster distance of 0.15, resulting in a threshold distance of 0.225. 
     If the distance between the current point and the nearest cluster is not within the threshold distance, the scanner determines whether the current point meets an unknown anomaly labeling criterion ( 741 ). The scanner can apply various unknown anomaly labeling criteria, such as a time period threshold criterion, an immediate change criterion, and a new cluster criteria. Applying the time period threshold criterion includes determining that the metrics of the current multivariate data slice collectively express an unknown anomalous behavior because 1) the current point cannot be assigned to any named anomaly cluster or a canonical cluster and 2) the scanner has not detected any canonical behaviors or known anomalies for at least a defined time period (also referred to as a time period threshold). For example, if the time period threshold is defined as 5 minutes, and the preceding multivariate data slice derived points within the previous 5 minutes are not part of any cluster, then the scanner determines that the unknown anomaly labeling criterion is met. If the unknown anomaly labeling criterion is met, then the scanner labels the current point as an unknown anomaly and generates an unknown anomaly event. Labeling a point can include associating an unknown anomaly tag with the point and adding the point to a data structure. Labeling a point can also include tagging a multivariate data slice with the unknown anomaly tag and storing the multivariate data slice in a separate data structure. The time period threshold can be any value greater than zero. The time period threshold is likely a multiple of the slice width. Applying the immediate change criterion is similar to applying the time period threshold criterion, except that the scanner immediately labels the current point as an unknown anomaly if the scanner has not detected any canonical behaviors or known anomalies without considering preceding multivariate data slice derived points. 
     Alternatively, or in addition, the scanner can apply new cluster criteria and determine that the current multivariate data slice is expressing behavior corresponding with an unknown anomaly when the current point forms a new cluster with previous outlier points. The scanner can establish the new cluster corresponding to an unknown anomaly (“unknown anomaly cluster”) based on the parameters used to train and update clusters of the anomaly and canonical models. For example, a new cluster can be defined as a set of points having at least n points, each within a pre-established maximum distance of each other and outside of a defined maximum distance of the already established clusters. If a cluster for canonical behavior is the only established cluster, and if n points are outside of the defined maximum distance of the cluster for canonical behavior, and if each point of then points are within a pre-established maximum distance of each other, then the scanner establishes a new unknown anomaly cluster from the n points. After the new cluster has been established as representing an unknown anomaly, a notification can be generated to investigate the cluster members and subsequent cluster analysis will include the established unknown anomaly cluster (i.e., the determination of distance ( 728 ) will include the unknown anomaly cluster). In the case of multiple unknown anomaly clusters, the anomaly detector will generate and assign distinguishing identifiers for the unknown anomaly clusters. 
     If the scanner determines that the current point meets the unknown anomaly labeling criteria, the scanner labels the current point as expressing an unknown anomaly ( 742 ). As described above, this “labeling” can involve different operations. For example, the labeling may be associating an unknown anomaly tag or indicator with the current point and/or corresponding multivariate data slice. If the anomaly detector is establishing unknown anomaly clusters, then the labeling can also include creation of the unknown anomaly cluster and assignment of the current point and previous qualifying points to the unknown anomaly cluster. If the current point does not meet the unknown anomaly labeling criteria, then the scanner updates the current multivariate data slice with measurements of a next time instant ( 764 ). The measurements of the feature set being monitored by the scanner should be read in or arrive at a rate that allows for consumption by the scanner. For instance, after completion of the cluster analysis, measurements of the next time instant are available for the scanner to read into the multivariate data slice data structure and push out the oldest time instant from the structure. As mentioned previously, implementations can coordinate the rate of retrieval/collection of monitored feature set measurements with analysis differently (e.g., creating the multivariate data slices based on the sliding slice width window asynchronously with the multivariate clustering analysis). 
     If the anomaly detector determines that the distance between the current point and the nearest cluster is within the threshold distance ( 740 ), the scanner labels the current point as expressing the behavior corresponding with the nearest cluster and determines if the behavior is a canonical behavior ( 744 ). For example, if the current point is nearest to a cluster labeled as “memory leak,” the scanner labels the current point as expressing the known anomaly “memory leak.” Because memory leak is not a canonical behavior, the scanner determines that the behavior is not canonical. As described above with reference to  FIG. 6 , the scanner generates an event indicating the detection of a memory leak anomaly. In addition, the scanner can update the cluster corresponding with the canonical/anomaly model to include the current point and determine a confidence for the inclusion. 
     After labeling the current point, the scanner determines a confidence for including the current point in the nearest cluster ( 748 ). The confidence can be calculated using various methods. One method is based on the distances between the current point and the nearest clusters. For example, when the distance between a current point and the nearest cluster C 1  is d 1  and the distance between a current point and the second-nearest cluster C 2  is d 2 , the normalized confidence that the point is correctly included in the cluster C 1  is Confidence(C 1 ), and can be determined as follows in Equation 1: 
     
       
         
           
             
               
                 
                   
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     After determining the behavior of the distributed application based on the current point, the scanner also determines whether the application behavior is transitioning from a first cluster to a second cluster ( 752 ). The system can determine that a cluster transition occurs if a past point was a part of a first cluster and a current point is both no longer part of the first cluster and is closer to a second cluster based on their respective distances from the current point. If not, the scanner does not determine a transition speed. Otherwise, the scanner determines a transition speed ( 760 ). The transition speed is determined based on a ratio between the distance traveled by the current point relative to the position of the point at a previous time instant. For example, if a current point has a distance of 0.60 normalized units from the preceding point (i.e., the interpoint distance is 0.60 normalized units) and the preceding point was measured at a time of 10 second before the current point, the transition speed is 0.06 normalized units/second. If an anomaly event is generated (i.e., the point has been assigned to a cluster representing an anomaly), then the transition speed can be included in the anomaly event. The transition speed can be used in root cause analysis of a corresponding anomaly. The transition speed may also be used for other analysis such as predicting when the behavior of the distributed application will be expressing behavior corresponding with the second cluster. For example, if a current point is moving at 0.06 normalized units/second towards a boundary of a cluster labeled with “memory leak” that 0.6 normalized units away, the scanner can provide a prediction that the distributed application is 10 seconds away from expressing the known anomaly “memory leak.” 
     Once the scanner has determined whether or not to label the current point as expressing the known behavior or an unknown anomaly, the scanner trains or updates the clustering analysis based on the current point. Training or updating the clustering analysis includes storing the current point into a history of points, forming new clusters based on the history of points, and labeling clusters based on known behaviors. The history of points includes some or all of the points transformed by the scanner. The scanner can process the history of points to determine if a new cluster should be formed. If the scanner first forms a new cluster, the scanner correlates the cluster to a canonical behavior or a known anomaly based on the result of the pattern analysis described above with reference to  FIG. 6 . For example, a scanner forming a new cluster can analyze the measurement times of the points in the new cluster and determine if they correspond with any canonical or anomaly models reported by the pattern analysis. Furthermore, alternative cluster labeling methods are described below with reference to  FIG. 9 . If the new cluster correlates with a known behavior, the new cluster is labeled as expressing the known behavior. In addition, the scanner can update a cluster for canonical behavior or known anomalies by adding the current point to the cluster. The scanner can update the centroid position of the cluster to account for the changes to the cluster centroid caused by the added point. 
       FIG. 8  is a visualization of cluster detection for points from a distributed application. Each of the points  821 - 827 ,  841 - 847 ,  855 , and  861 - 866  in  FIG. 8  represents a particular point having a position determined by the elements of a principal component of a multivariate data slice, and the axes of the plot in  FIG. 8  are PCA axes. The principal components are based on multivariate data slices. For example, the principal components can be based on multivariate data slices that include the application related metrics “InitiationA.AvgRespT,” “PurchaseNode.AvgRespT,” and “DB1.ErrPerIntvl.” The points  821 - 827  are part of the cluster  820 . The points  841 - 847  are part of the cluster  840 . The points  861 - 866  are part of the cluster  860 . In addition, the points  805 ,  806 , and  855  are not a part of clusters  820 ,  840 , or  860 . Each of the points in the figure can be collectively analyzed using various clustering algorithms (K-means, Fuzzy-C means, Hierarchical, etc.). 
     The clusters can be labeled based on a comparison with pattern analysis results. For example, points in the cluster  820  correspond with pattern analysis results that report the metrics of the points as expressing canonical behavior. In response, the cluster  820  is labeled with a label indicating “canonical behavior.” Alternatively, the cluster can be labeled based on one or more points in a history of labeled points. Each point in a cluster storing the labeled points can be assigned the same label. These labeled points can be used to label the entire cluster. For example, each of the points  845 - 846  and  865 - 866  are loaded upon initialization of the scanner and respectively labeled as expressing the known anomalies “memory leak” and “death by a thousand cuts.” These names enable the scanner to intelligently label each of the clusters  840  and  860  with their respective names of “memory leak” and “death by a thousand cuts.” 
     When a current point is generated based on a current multivariate data slice, it is added to the set of points for cluster analysis. If the scanner determines that distance of a newly-generated point from the nearest cluster is within a distance threshold, then the scanner determines that the newly-generated point is a part of the cluster. Based on this determination, the application behavior corresponding with the cluster is associated with the time/time period of the newly-generated point. For example, if the point  827  is the current point and the scanner determines that the distance between the point  827  and the cluster  820  is within a threshold distance, the scanner will determine that the current point  827  is part of the cluster  820 . In response, the scanner determines that the current point  827  is part of the cluster  820  and that the current behavior is the behavior expressed by the cluster  820 . For example, if the cluster  820  is labeled with the anomaly name “memory leak,” then the scanner determines that the distributed application is expressing behavior correlated with a memory leak. 
     With reference to  FIG. 7  described above, the scanner can apply the time period threshold criterion as a unknown anomaly labeling criterion to detect an unknown anomaly. For example, if the point  806  is the current point, the scanner determines that the distances between the current point  806  and each of the clusters  820 ,  840 , and  860  are beyond a distance threshold and thus the scanner has not detected any canonical behaviors or known anomalies for the time instant corresponding to the current point. The scanner also determines that the distance between the current point  805  and each of the clusters  820 ,  840 , and  860  are beyond the distance threshold and thus has not detected any canonical behaviors or known anomalies for the time instant corresponding to the point  805 . If the time period threshold is 5 minutes, and if the point  805  is the only preceding multivariate data slice derived point within the previous 5 minutes, then the scanner determines the point  806  is not in any cluster and that the unknown anomaly labeling criterion is met. In response, the scanner labels the point  806  as expressing an unknown anomaly and generates an unknown anomaly event. 
     With continued reference to  FIG. 7 , an unknown anomaly can be detected when a current point is part of a new cluster if the scanner applies the new cluster criteria described above for the unknown anomaly labeling criteria. For example, if new clusters are defined as a set of points having at least three points within a pre-established distance from each other, and if the points  805 ,  806 , and  855  are each outside of a defined maximum distance of the already established clusters, then the scanner combines the points  805 ,  806 , and  855  to establish a new cluster including the three points as an unknown anomaly cluster. After the new cluster is established, the scanner generates a notification to investigate the cluster members. 
       FIG. 9  illustrates a flowchart of example operations to train and label clusters for an anomaly detector. The example operations of  FIG. 9  represent the operations performed by instantiated scanners and can be performed either before or in coordination with the operations described above with reference to  FIG. 7 . The description of  FIG. 9  refers to a scanner as performing the example operations. The example operations presume the scanner has already generated a set of points corresponding to multivariate data of a feature set selected based on the topology of a distributed application. 
     Based on data available to an anomaly detector, the scanner deploys an initial training dataset with defined canonical and anomaly models to a history of points ( 906 ). The history of points includes at least a minimum training number of available points for training the anomaly detector. The defined canonical and anomaly models include information corresponding to one or more clusters that express known behaviors. The information can include laboratory datasets generated based on the defined models or historical datasets from similar distributed applications. In addition to using initial training data, the scanner collects and transforms a multivariate data slice into a current point and adds the current point to the history of points ( 920 ). The scanner proceeds to determine the clusters and cluster centroids based on the history of points ( 928 ). Determining the clusters involves determining that one or more of the points in the history of points are part of a cluster and can be performed using various cluster analysis techniques. For example, the scanner can use a K-means clustering method to determine the existence of distinct clusters. 
     For each cluster ( 932 ), the scanner determines whether the cluster is already labeled based on a defined canonical or anomaly model ( 934 ). The defined canonical or anomaly model corresponds with a known behavior and includes one or more points expressing the known behavior. If the point(s) expressing the known behavior is part of a cluster, the scanner establishes the cluster as expressing the known behavior ( 938 ). For example, the scanner labels a cluster as expressing a memory leak if the cluster includes a point labeled as expressing a “memory leak” from a defined anomaly model. Once the cluster is established, the scanner determines if there are additional clusters to be processed, described further below ( 940 ). 
     If the cluster is not already labeled based on a defined canonical or anomaly model, the scanner determines whether the cluster corresponds with a canonical behavior or a known anomaly based on pattern detection ( 936 ). When a pattern is detected from multivariate data slices using the pattern detection methods disclosed above with reference to  FIG. 4 , the points generated from the multivariate data slices correspond with a canonical behavior or a known anomaly based on pattern detection. For example, if the measurements in a set of multivariate data slices fit the set of functions indicating canonical behavior within a specified margin of variance, the scanner labels the cluster of corresponding points as expressing the canonical behavior, wherein each of the corresponding points are transformed from one of the fitting multivariate data slices. In addition, the margin of variance can be changed (e.g., tightened/decreased or loosened/increased) in order to modify cluster sizes and the number of points in a cluster expressing a known behavior. If the scanner determines the cluster corresponds with either a canonical behavior or a known anomaly based on pattern detection, the scanner will establish the cluster as expressing the canonical behavior or a known anomaly ( 938 ). 
     After determining whether or not to establish the cluster as expressing a canonical behavior or a known anomaly, the scanner determines if there are additional clusters to be processed ( 940 ). If so, the scanner processes the additional cluster and labels the additional cluster if appropriate. Otherwise, the scanner finishes training by generating or updating canonical and anomaly models based on the one or more clusters ( 944 ). Generating and updating canonical and anomaly models based on one or more clusters includes establishing a new cluster and updating one or more clusters using the operations described above with reference to  FIG. 7 . 
     Variations 
     The above example illustrations describe generating an anomaly event when a point is assigned to an anomaly cluster. Embodiments, however, can also generate an event when a point is assigned to a canonical cluster based on an assumption that preceding behavior was not canonical. If preceding behavior was not canonical, then preceding multivariate data slices representing that preceding behavior can be referenced or indicated in an event for analysis. 
     The flowcharts are provided to aid in understanding the illustrations and are not to be used to limit scope of the claims. The flowcharts depict example operations that can vary within the scope of the claims. Additional operations may be performed; fewer operations may be performed; the operations may be performed in parallel; and the operations may be performed in a different order. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by program code. The program code may be provided to a processor of a general purpose computer, special purpose computer, or other programmable machine or apparatus. In addition, while points are determined from the transformation of multivariate data slice, points can also be determined based on measurements from individual time instants. 
     Machine-Readable Media and Example Computer System 
     As will be appreciated, aspects of the disclosure may be embodied as a system, method or program code/instructions stored in one or more machine-readable media. Accordingly, aspects may take the form of hardware, software (including firmware, resident software, micro-code, etc.), or a combination of software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” The functionality presented as individual modules/units in the example illustrations can be organized differently in accordance with any one of platform (operating system and/or hardware), application ecosystem, interfaces, programmer preferences, programming language, administrator preferences, etc. 
     Any combination of one or more machine-readable medium(s) may be utilized. The machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. A machine-readable storage medium may be, for example, but not limited to, a system, apparatus, or device, that employs any one of or combination of electronic, magnetic, optical, electromagnetic, infrared, or semiconductor technology to store program code. More specific examples (a non-exhaustive list) of the machine-readable storage medium would include the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a machine-readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. A machine-readable storage medium is not a machine-readable signal medium. 
     A machine-readable signal medium may include a propagated data signal with machine-readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A machine-readable signal medium may be any machine-readable medium that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device, but is not a machine-readable storage medium. 
     Program code embodied on a machine-readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing. 
     Computer program code for carrying out operations for aspects of the disclosure may be written in any combination of one or more programming languages, including an object oriented programming language such as the Java® programming language, C++ or the like; a dynamic programming language such as Python; a scripting language such as Perl programming language or PowerShell script language; and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on a stand-alone machine, may execute in a distributed manner across multiple machines, and may execute on one machine while providing results and or accepting input on another machine. 
     The program code/instructions may also be stored in a machine-readable medium that can direct a machine to function in a particular manner, such that the instructions stored in the machine-readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
       FIG. 10  depicts an example computer system with a multivariate clustering-based anomaly detector. The computer system includes a processor  1001  (possibly including multiple processors, multiple cores, multiple nodes, and/or implementing multi-threading, etc.). The computer system includes memory  1007 . The memory  1007  may be system memory (e.g., one or more of cache, SRAM, DRAM, zero capacitor RAM, Twin Transistor RAM, eDRAM, EDO RAM, DDR RAM, EEPROM, NRAM, RRAM, SONOS, PRAM, magnetic memory, etc.) or any one or more of the above already described possible realizations of machine-readable media. The computer system also includes a bus  1003  (e.g., PCI, ISA, PCI-Express, HyperTransport® bus, InfiniBand® bus, NuBus, etc.) and a network interface  1005  (e.g., a Fiber Channel interface, an Ethernet interface, an internet small computer system interface, SONET interface, wireless interface, etc.). The system also includes an anomaly detector  1011 . The anomaly detector  1011  scans multivariate data slices of an application component(s) in a transaction execution path to detect anomalies. The anomaly detector  1011  selects metrics at least based on the transaction execution path. So, metrics of components of a distributed application that are not active (i.e., not within the execution path) are not scanned. The anomaly detector  1011  uses multivariate clustering analysis to determine whether a behavior of a distributed application is canonical behavior, a known anomaly, or an unknown anomaly. The computational efficiency can be further increased by transforming the metric data slices to vectors/points. Any one of the previously described functionalities may be partially (or entirely) implemented in hardware and/or on the processor  1001 . For example, the functionality may be implemented with an application specific integrated circuit, in logic implemented in the processor  1001 , in a co-processor on a peripheral device or card, etc. The processor  1001  and the network interface  1005  are coupled to the bus  1003 . Although illustrated as being coupled to the bus  1003 , the memory  1007  may be coupled to the processor  1001 . 
     While the aspects of the disclosure are described with reference to various implementations and exploitations, it will be understood that these aspects are illustrative and that the scope of the claims is not limited to them. In general, techniques for multivariate clustering analysis of sets of application related metrics to detect anomalies for a distributed application as described herein may be implemented with facilities consistent with any hardware system or hardware systems. Many variations, modifications, additions, and improvements are possible. 
     Plural instances may be provided for components, operations or structures described herein as a single instance. Finally, boundaries between various components, operations and data stores are somewhat arbitrary, and particular operations are illustrated in the context of specific illustrative configurations. Other allocations of functionality are envisioned and may fall within the scope of the disclosure. In general, structures and functionality presented as separate components in the example configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the disclosure. 
     Use of the phrase “at least one of” preceding a list with the conjunction “and” should not be treated as an exclusive list and should not be construed as a list of categories with one item from each category, unless specifically stated otherwise. A clause that recites “at least one of A, B, and C” can be infringed with only one of the listed items, multiple of the listed items, and one or more of the items in the list and another item not listed.