Prometheus probe

Prometheus probe allows users to run Prometheus queries and match the resulting output against specific conditions. The intent behind this probe is to allow users to define metrics-based SLOs in a declarative way and determine the experiment verdict based on its success. The probe runs the query on a Prometheus server defined by the endpoint, and checks whether the output satisfies the specified criteria. A PromQL query needs to be provided, whose outcome is then used for the probe validation.

YAML only feature

In case of complex queries that span multiple lines, the queryPath attribute can be used to provide the link to a file consisting of the query. This file can be made available in the experiment pod via a ConfigMap resource, with the ConfigMap being passed in the ChaosEngine or the ChaosExperiment CR. Also, query and queryPath attributes are mutually exclusive. Refer to the probe schema here.

Defining the probe

You can define the probes at .spec.experiments[].spec.probe path inside the chaos engine.

kind: Workflow
apiVersion: argoproj.io/v1alpha1
spec:
  templates:
    - inputs:
        artifacts:
          - raw:
              data: |
                apiVersion: litmuschaos.io/v1alpha1
                kind: ChaosEngine
                spec:
                  experiments:
                    - spec:
                        probe:
                          ####################################
                          Probes are defined here
                          ####################################

Schema

Listed below is the probe schema for the Prometheus probe, with properties shared across all the probes and properties unique to the Prometheus probe.

Field	Description	Type	Range	Notes
name	Flag to hold the name of the probe	Mandatory	N/A `type: string`	The `name` holds the name of the probe. It can be set based on the usecase
type	Flag to hold the type of the probe	Mandatory	`httpProbe, k8sProbe, cmdProbe, promProbe`	The `type` supports four types of probes. It can one of the httpProbe, k8sProbe, cmdProbe, promProbe
mode	Flag to hold the mode of the probe	Mandatory	`SOT, EOT, Edge, Continuous, OnChaos`	The `mode` supports five modes of probes. It can one of the SOT, EOT, Edge, Continuous, OnChaos
endpoint	Flag to hold the prometheus endpoints for the promProbe	Mandatory	N/A `type: string`	The `endpoint` contains the prometheus endpoints
query	Flag to hold the promql query for the promProbe	Mandatory	N/A `type: string`	The `query` contains the promql query to extract out the desired prometheus metrics via running it on the given prometheus endpoint
queryPath	Flag to hold the path of the promql query for the promProbe	Optional	N/A `type: string`	The `queryPath` field is used in case of complex queries that spans multiple lines, the queryPath attribute can be used to provide the path to a file consisting of the same. This file can be made available to the experiment pod via a ConfigMap resource, with the ConfigMap name being defined in the ChaosEngine OR the ChaosExperiment CR.

Comparator

Field	Description	Type	Range	Notes
type	Flag to hold type of the data used for comparison	Optional	`float`	The `type` contains type of data, which should be compared as part of comparison operation. Prometheus probe only compares with float data.
criteria	Flag to hold criteria for the comparison	Mandatory	It supports `>=, <=, ==, >, <, !=, oneOf, between` for int & float type. And `equal, notEqual, contains, matches, notMatches, oneOf` for string type.	The `criteria` contains criteria of the comparison, which should be fulfill as part of comparison operation.
value	Flag to hold value for the comparison	Mandatory	N/A `type: string`	The `value` contains value of the comparison, which should follow the given criteria as part of comparison operation.

Authentication

This establishes a fundamental authentication mechanism for the Prometheus server. The username:password, encoded in base64, should be placed either within the credentials field or as a file path in the credentialsFile field. It's important to note that credentials and credentialsFile are two options that cannot be used simultaneously.

Field	Description	Type	Range	Notes
credentials	Flag to hold the basic auth credentials in base64 format	Optional	`string`	The `credentials` comprises the Prometheus server's basic authentication credentials in the form of username:password, encoded using base64 format
credentialsFile	Flag to hold the basic auth credentials file path	Optional	`string`	The `credentials` encompasses the filepath for basic authentication credentials, which are mounted to the experiment pod as volume secrets. These secrets consist of username:password encoded in base64 format for the Prometheus server

TLS

It offers the mechanism to validate TLS certifications for the Prometheus server. You can supply the cacert or the client certificate and client key, to perform the validation. Alternatively, you have the option to enable the insecureSkipVerify check to bypass certificate validation.

Field	Description	Type	Range	Notes
caFile	Flag to hold the ca file path	Optional	`string`	The `caFile` holds the file path of the CA certificates utilized for server TLS verification
certFile	Flag to hold the client cert file path	Optional	`string`	The `certFile` holds the file path of the client certificates utilized for TLS verification
keyFile	Flag to hold the client key file path	Optional	`string`	The `keyFile` holds the file path of the client key utilized for TLS verification
insecureSkipVerify	Flag to skip the tls certificates checks	Optional	`boolean`	The `insecureSkipVerify` skip the tls certificates checks

Run properties

Field	Description	Type	Range	Notes
probeTimeout	Flag to hold the timeout of the probe	Mandatory	N/A `type: string`	The `probeTimeout` represents the time limit for the probe to execute the specified check and return the expected data
attempt	Flag to hold the attempt of the probe	Mandatory	N/A `type: integer`	The `attempt` contains the number of times a check is run upon failure in the previous attempts before declaring the probe status as failed.
interval	Flag to hold the interval of the probe	Mandatory	N/A `type: string`	The `interval` contains the interval for which probes waits between subsequent retries
probePollingInterval	Flag to hold the polling interval for the probes (applicable for all modes)	Optional	N/A `type: string`	The `probePollingInterval` contains the time interval for which continuous and onchaos probe should be sleep after each iteration
initialDelaySeconds	Flag to hold the initial delay interval for the probes	Optional	N/A `type: integer`	The `initialDelaySeconds` represents the initial waiting time interval for the probes.
stopOnFailure	Flags to hold the stop or continue the experiment on probe failure	Optional	N/A `type: boolean`	The `stopOnFailure` can be set to true/false to stop or continue the experiment execution after probe fails

Definition

probe:
  - name: "check-probe-success"
    type: "promProbe"
    promProbe/inputs:
      endpoint: "prometheus-server.prometheus.svc.cluster.local:9090"
      query: "sum(rate(http_requests_total{code=~\"2..\"}[1m])) by (job)"
      comparator:
        criteria: ">" #supports >=,<=,>,<,==,!= comparison
        value: "0"
      auth:
        credentials: "base64(<username:password>)"
      tlsConfig:
        insecureSkipVerify: true
    mode: "Edge"
    runProperties:
      probeTimeout: 5s
      interval: 2s
      attempt: 1

Prometheus Query(query is a simple)

This section holds the PromQL query used to extract the desired Prometheus metrics by executing it on the specified Prometheus endpoint. You can input the Prometheus query in the 'query' field, and this can be initiated by configuring the .promProbe/inputs.query field.