Litmus chaos-scheduler for injecting chaos experiments on Kubernetes

Litmus chaos scheduler 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 scheduler, the operator & Experiment custom resource bundles via helm charts
Annotate the application under test (AUT), enabling it for chaos
Create a ChaosSchedule custom resource, which describes the ChaosEngine template to be scheduled

What is a chaos scheduler and how is it built?

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

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

What is a chaos schedule?

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

Execution Schedule for the batch run of the experiments
Template Spec of ChaosEngine according to which chaos is to be exceuted

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

Sample ChaosSchedule for reference:

apiVersion: litmuschaos.io/v1alpha1
kind: ChaosSchedule
metadata:
name: schedule-nginx
namespace: litmus
spec:
schedule:
  repeat:
    executionTime: "2020-05-11T20:30:00Z"   #should be set for type=once
    startTime: "2020-05-12T05:47:00Z"   #should be modified according to current UTC Time
    endTime: "2020-05-12T05:52:00Z"   #should be modified according to current UTC Time
    minChaosInterval: "2m"   #format should be like "10m" or "2h" accordingly for minute and hours
    instanceCount: "2"
    includedDays: "Mon,Tue,Wed"
engineTemplateSpec:
  appinfo:
    appns: 'default'
    applabel: 'app=nginx'
    appkind: 'deployment'
  # It can be true/false
  annotationCheck: 'true'
  #ex. values: ns1:name=percona,ns2:run=nginx
  auxiliaryAppInfo: ''
  chaosServiceAccount: pod-delete-sa
  monitoring: false
  # It can be delete/retain
  jobCleanUpPolicy: 'delete'
  experiments:
    - name: pod-delete
      spec:
        components:
          env:
            # set chaos duration (in sec) as desired
            - name: TOTAL_CHAOS_DURATION
              value: '30'

            # set chaos interval (in sec) as desired
            - name: CHAOS_INTERVAL
              value: '10'

            # pod failures without '--force' & default terminationGracePeriodSeconds
            - name: FORCE
              value: 'false'

What is a chaos engine?

Refer

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

Refer

What are the steps to get started?

Install Operator Components and RBAC and CRDs

kubectl apply -f https://litmuschaos.github.io/pages/litmus-operator-latest.yaml

Install Scheduler and it's CRDs

kubectl apply -f https://raw.githubusercontent.com/litmuschaos/chaos-scheduler/master/deploy/crds/chaosschedule_crd.yaml

kubectl apply -f https://raw.githubusercontent.com/litmuschaos/chaos-scheduler/master/deploy/chaos-scheduler.yaml

Create the pod delete Chaos Experiment in default namespace

kubectl apply -f https://raw.githubusercontent.com/litmuschaos/chaos-charts/1.4.0/charts/generic/pod-delete/experiment.yaml

Create the RBAC for execute the pod-delete chaos

kubectl apply -f https://raw.githubusercontent.com/litmuschaos/chaos-charts/1.4.0/charts/generic/pod-delete/rbac.yaml

Annotate your application to enable chaos. For ex:

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

Create a ChaosSchedule yaml with the application information and chaos experiment with their scheduling logic, For example: Click Here
Create a ChaosSchedule customer resource in the desired cluster, For example
```
kubectl apply -f chaos-schedule.yaml
```
Watch the injection of chaos at the scheduled time, For example
```
watch kubectl get pod,chaosschedule,chaosengine -n litmus
```

Describe the ChaosSchedule for see the detail of chaos injection.

kubectl describe chaosschedule schedule-nginx

Refer the ChaosSchedule Status. While any ChaosEngine is active or yet to be formed according to the schedule time. The .status.schedule.status is set to running eventually changed to completed

Name:         schedule-nginx
Namespace:    default
Labels:       <none>
Annotations:  API Version:  litmuschaos.io/v1alpha1
Kind:         ChaosSchedule
Metadata:
  Creation Timestamp:  2020-05-14T08:44:32Z
  Generation:          3
  Resource Version:    899464
  Self Link:           /apis/litmuschaos.io/v1alpha1/namespaces/default/chaosschedules/  schedule-nginx
  UID:                 347fb7e6-2c9d-428e-9ce1-42bdcfdab37d
Spec:
  Chaos Service Account:  
  Engine Template Spec:
    Appinfo:
      Appkind:              deployment
      Applabel:             app=nginx
      Appns:                default
    Chaos Service Account:  litmus
    Components:
      Runner:
    Experiments:
      Name:  pod-delete
      Spec:
        Components:
        Rank:             0
    Job Clean Up Policy:  retain
  Schedule:
    Repeat:
      End Time:            2020-05-12T05:52:00Z
      Included Days:       Mon,Tue,Wed
      Instance Count:      2
      Min Chaos Interval:  2m
      Start Time:          2020-05-12T05:47:00Z
  Schedule State:        active
Status:
  Active:
    API Version:       litmuschaos.io/v1alpha1
    Kind:              ChaosEngine
    Name:              schedule-nginx
    Namespace:         default
    Resource Version:  899463
    UID:               14f49857-8879-4129-a5b9-a3a592149725
  Last Schedule Time:  2020-05-14T08:44:32Z
  Schedule:
    Start Time:              2020-05-14T08:44:32Z
    Status:                  running
    Total Instances:         1
Events:
  Type    Reason            Age   From             Message
  ----    ------            ----  ----             -------
  Normal  SuccessfulCreate  39s   chaos-scheduler  Created engine schedule-nginx

How to halt the chaosschedule?

Edit the applied chaosschedule

kubectl edit chaosschedule schedule-nginx

Change the state to halt
```
spec:
  scheduleState: halt
```

How to resume the chaosschedule?