Command probe

This topic describes the definition and schema of the command probe. It also describes how to tune the probe in two modes: inline mode and source mode.

The command probe allows you to run Bash commands and match the output as part of the entry or exit criteria. The intent behind this probe is to implement a non-standard and imperative way to express the hypothesis. For example, you can check for specific data within a database, parse the value out of a JSON blob that is dumped into a certain path, or check for the existence of a particular string in the service logs.

YAML only feature

By default, this probe can be defined in inline mode from the user interface, where the command is run from within the experiment image. It can also be run in source mode, where the command execution is carried out from within a new pod whose image is specified. Inline mode is preferred for simple shell commands, and source mode is preferred when application-specific binaries are required.

Probe definition

You can define the probe 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
                          ####################################

tip

The command probe expects you to provide a shell command to implement checks that are highly specific to the application use case.

Schema

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

Field	Description	Type	Range	Notes
name	Flag that holds 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 use-case
type	Flag to hold the type of the probe	Mandatory	httpProbe, k8sProbe, cmdProbe, promProbe, and datadogProbe	The type supports five types of probes: httpProbe, k8sProbe, cmdProbe, promProbe, and datadogProbe.
mode	Flag to hold the mode of the probe	Mandatory	SOT, EOT, Edge, Continuous, OnChaos	The mode supports five modes of probes: SOT, EOT, Edge, Continuous, and OnChaos. Datadog probe supports EOT mode only.
command	Flag to hold the command for the cmdProbe	Mandatory	N/A type: string	The command contains the shell command, which should be run as part of cmdProbe

Source

Field	Description	Type	Range	Notes
image	Flag to hold the image for the cmdProbe	Mandatory	any source docker image	The image provides the source image which can be used to launch a external pod where the command execution is carried out.
hostNetwork	Flag to allow or deny the image access to the node network namespace	Optional	true, false	The hostNetwork provides a possibility to allow the pod executing the cmdProbe access to the network of the node he is running on. For more details, go to the official Kubernetes documentation.
inheritInputs	Flag for inheriting experiment pod attributes such as ENV, volumes, and volumeMounts into the probe pod	Optional	true, false	Default is false i.e. the experiment pod attributes won't be inherited by the probe pod by default
args	Arguments to be used for the source probe	Optional	type: string	List of arguments to be used along with the probe command
env	Environment variables to be used for the source probe pod	Optional	type: string	List of environment variables to be used probe pod container
labels	Labels for the source probe pod	Optional	type: string	Labels to be added to the source probe pod
annotations	Annotations for the source probe pod	Optional	type: string	Annotations to be added to the source probe pod
command	Command to be executed using the source probe image	Optional	type: string	Command to be executed using the source probe image, which can be provided as a list
imagePullPolicy	Image Pull Policy to be used for the source pod image	Optional	type: string	Image Pull Policy to be used for the source pod image, supports Always, IfNotPresent, and Never
privileged	Privileged execution permissions for the probe image	Optional	true, false	Privileged execution permissions for the probe image, supports a boolean value
nodeSelector	Label(s) of the node(s) to be used for deploying the source probe pod	Optional	type: string	Key-Value label(s) of the node(s) to be used for deploying the source probe pod
volumes	Volumes to be mounted to the source probe pod	Optional	N/A	Depending on the type of the volume, additional properties need to be provided
volumesMount	Volume mount paths for the corresponding source pod volumes	Optional	type: string	List of volume mount paths for the corresponding source pod volumes
imagePullSecrets	Image pull secrets for the source pod image	Optional	type: string	List of image pull secrets for the source pod image

Comparator

Field	Description	Type	Range	Notes
type	Flag to hold type of the data used for comparison	Mandatory	string, int, float	The type contains type of data, which should be compared as part of comparison operation.
criteria	Flag to hold criteria for the comparison	Mandatory	It supports >=, <=, ==, >, <, !=, oneOf, between for int and 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.

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-database-integrity"
    type: "cmdProbe"
    cmdProbe/inputs:
      command: "<command>"
      comparator:
        type: "string" # supports: string, int, float
        criteria: "contains" #supports >=,<=,>,<,==,!= for int and float, and contains, equal, notEqual, matches, notMatches, oneOf for string values
        value: "<value-for-criteria-match>"
      source: # omit this tag to "inline" the probe
        image: "<repo>/<tag>"
        hostNetwork: false
    mode: "Edge"
    runProperties:
      probeTimeout: 5
      interval: 5
      retry: 1
      initialDelaySeconds: 5

Inline mode

In the inline mode, the command probe is executed directly within the experiment pod. This mode is recommended for executing straightforward shell commands. It is the default mode and can be tuned by leaving out the 'source' field.

Use the following example to tune this:

# execute the command inside the experiment pod itself
# cases where command doesn't need any extra binaries, which is not available in the experiment image
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  appinfo:
    appns: "default"
    applabel: "app=nginx"
    appkind: "deployment"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: pod-delete
    spec:
      probe:
      - name: "check-database-integrity"
        type: "cmdProbe"
        cmdProbe/inputs:
          # command which needs to run in cmdProbe
          command: "echo 'hello world'"
          comparator:
            # output type for the above command
            # supports: string, int, float
            type: "string"
            # criteria which should be followed by the actual output and the expected output
            #supports [>=, <=, >, <, ==, !=] for int and float
            # supports [contains, equal, notEqual, matches, notMatches, oneOf] for string values
            criteria: "contains"
            # expected value, which should follow the specified criteria
            value: "hello"
        mode: "Edge"
        runProperties:
          probeTimeout: 5s
          interval: 2s
          attempt: 1

Source Mode

In source mode, the command is executed within a newly created pod, allowing for the specification of its image. This mode is useful when application-specific binaries are needed.

Use the following example to tune this:

# it launches the external pod with the source image and run the command inside the same pod
# cases where command needs an extra binaries which is not available in the experiment image
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  appinfo:
    appns: "default"
    applabel: "app=nginx"
    appkind: "deployment"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: pod-delete
    spec:
      probe:
      - name: "check-database-integrity"
        type: "cmdProbe"
        cmdProbe/inputs:
          # command which needs to run in cmdProbe
          command: "<command>"
          comparator:
            # output type for the above command
            # supports: string, int, float
            type: "string"
            # criteria which should be followed by the actual output and the expected output
            #supports [>=, <=, >, <, ==, !=, oneOf, between] for int and float
            # supports [contains, equal, notEqual, matches, notMatches, oneOf] for string values
            criteria: "contains"
            # expected value, which should follow the specified criteria
            value: "<value-for-criteria-match>"
          # source for the cmdProbe
          source:
            image: "<source-image>"
            imagePullPolicy: Always
            privileged: true
            hostNetwork: false
        mode: "Edge"
        runProperties:
          probeTimeout: 5s
          interval: 2s
          attempt: 1