Litmus chaos-operator for injecting chaos experiments on Kubernetes

Litmus chaos operator is used by Kubernetes application developers and SREs to inject chaos into the applications and Kubernetes infrastructure in a managed fashion. Its objective is to make the process of validation and hardening of application workloads on Kubernetes easy by automating the execution of chaos experiments. A sample chaos injection workflow could be as simple as:

• Install the Litmus infrastructure components (RBAC, CRDs), the Operator & Experiment custom resource bundles via helm charts
• Annotate the application under test (AUT), enabling it for chaos
• Create a ChaosEngine custom resource tied to the AUT, which describes the experiment list to be executed

Benefits provided by the Chaos Operator include:

• Scheduled batch Run of Chaos
• Standardised chaos experiment spec
• Categorized chaos bundles for stateless/stateful/vendor-specific
• Test-Run resiliency
• Ability to chaos run as a background service based on annotations

What is a chaos operator and how is it built?

The Chaos Operator is a Kubernetes Operator, which are nothing but custom-controllers with direct access to Kubernetes API that can manage the lifecycle of certain resources or applications, while always trying to ensure the resource is in the "desired state". The logic that ensures this is commonly called "reconcile" function.

The Chaos Operator is built using the popular Operator-SDK framework, which provides bootstrap support for new operator projects, allowing teams to focus on business/operational logic.

The Litmus Chaos Operator helps reconcile the state of the ChaosEngine, a custom resource that holds the chaos intent specified by a developer/devops engineer against a particular stateless/stateful Kubernetes deployment. The operator performs specific actions upon CRUD of the ChaosEngine, its primary resource. The operator also defines secondary resources (the engine runner pod and engine monitor service), which are created & managed by it in order to implement the reconcile functions.

What is a chaos engine?

The ChaosEngine is the core schema that defines the chaos workflow for a given application. Currently, it defines the following:

• Application Data (namespace, labels, kind)
• List of Chaos Experiments to be executed
• Attributes of the experiments, such as, rank/priority
• Execution Schedule for the batch run of the experiments

The ChaosEngine is the referenced as the owner of the secondary (reconcile) resource with Kubernetes deletePropagation ensuring these also are removed upon deletion of the ChaosEngine CR.

Here is a sample ChaosEngineSpec for reference:

apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  appinfo: 
    appns: default
    applabel: "app=nginx"
  experiments:
    - name: pod-delete 
      spec:
        rank: 
    - name: container-kill
      spec:
        rank:  

What is a litmus chaos chart and how can I use it?

Litmus Chaos Charts are used to install "Chaos Experiment Bundles" & are categorized based on the nature of the experiments (general Kubernetes chaos, vendor/provider specific chaos - such as, OpenEBS or application-specific chaos, say NuoDB). They consist of custom resources that hold low-level chaos(test) parameters which are queried by the operator in order to execute the experiments. The spec.definition.fields and their corresponding values are used to construct the eventual execution artifact that runs the chaos experiment (typically, the litmusbook, which is a K8s job resource).

Here is a sample ChaosEngineSpec for reference:

apiVersion: litmuschaos.io/v1alpha1
description:
  message: |
    Deletes a pod belonging to a deployment/statefulset/daemonset
kind: ChaosExperiment
metadata:
  labels:
    helm.sh/chart: k8sChaos-0.1.0
    litmuschaos.io/instance: dealing-butterfly
    litmuschaos.io/name: k8sChaos
  name: pod-delete
spec:
  definition:
    image: openebs/ansible-runner:ci
    litmusbook: /experiments/chaos/kubernetes/pod_delete/run_litmus_test.yml
    labels:
      name: pod-delete
    args:
    - -c
    - ansible-playbook ./experiments/chaos/kubernetes/pod_delete/test.yml -i /etc/ansible/hosts
      -vv; exit 0
    command:
    - /bin/bash
    env:
    - name: ANSIBLE_STDOUT_CALLBACK
      value: null
    - name: TOTAL_CHAOS_DURATION
      value: 15
    - name: CHAOS_INTERVAL
      value: 5
    - name: LIB
      value: ""

What are the steps to get started?

• Install Litmus infrastructure (RBAC, CRD, Operator) components

  helm repo add litmuschaos https://litmuschaos.github.io/chaos-charts
  helm repo update
  helm install litmuschaos/litmus --namespace=litmus
  

• Download the desired Chaos Experiment bundles, say, general Kubernetes chaos

  helm install litmuschaos/k8sChaos
  

• Annotate your application to enable chaos. For ex:

  kubectl annotate deploy/nginx-deployment litmuschaos.io/chaos="true"
  

• Create a ChaosEngine CR with application information & chaos experiment list with their respective attributes

  # engine-nginx.yaml is a chaosengine manifest file
  kubectl apply -f engine-nginx.yaml
  

• Refer the ChaosEngine Status (or alternately, the corresponding ChaosResult resource) to know the status of each experiment. The spec.verdict is set to Running when the experiment is in progress, eventually changing to pass or fail.

  kubectl describe chaosresult engine-nginx-pod-delete
  
  Name:         engine-nginx-pod-delete
  Namespace:    default
  Labels:       <none>
  Annotations:  kubectl.kubernetes.io/last-applied-configuration:
                {"apiVersion":"litmuschaos.io/v1alpha1","kind":"ChaosResult","metadata":{"annotations":{},"name":"engine-nginx-pod-delete","namespace":"de...
  API Version:  litmuschaos.io/v1alpha1
  Kind:         ChaosResult
  Metadata:
    Creation Timestamp:  2019-05-22T12:10:19Z
    Generation:          9
    Resource Version:    8898730
    Self Link:           /apis/litmuschaos.io/v1alpha1/namespaces/default/chaosresults/engine-nginx-pod-delete
    UID:                 911ada69-7c8a-11e9-b37f-42010a80019f
  Spec:
    Experimentstatus:
      Phase:    <nil>
      Verdict:  pass
  Events:       <none>
  

Where are the docs?

They are available at litmus docs

How do I contribute?

The Chaos Operator is in alpha stage and needs all the help you can provide! Please contribute by raising issues, improving the documentation, contributing to the core framework and tooling, etc.