litmus-docs/website/versioned_docs/version-1.8.0/pod-autoscaler.md

id	title	sidebar_label	original_id
pod-autoscaler	Scale the application replicas and test the node autoscaling on cluster	Pod Autoscaler	pod-autoscaler

---

Experiment Metadata

Type	Description	Tested K8s Platform
Generic	Scale the application replicas and test the node autoscaling on cluster	GKE, EKS, Minikube

Prerequisites

• Ensure that the Litmus Chaos Operator is running by executing kubectl get pods in operator namespace (typically, litmus). If not, install from here
• Ensure that the pod-autoscaler experiment resource is available in the cluster by executing kubectl get chaosexperiments in the desired namespace. If not, install from here

Entry Criteria

• Application pods are healthy on the respective Nodes before chaos injection

Exit Criteria

• Application pods will be healthy post chaos injection

Details

• The experiment aims to check the ability of nodes to accommodate the number of replicas a given application pod.

• This experiment can be used for other scenarios as well, such as for checking the Node auto-scaling feature. For example, check if the pods are successfully rescheduled within a specified period in cases where the existing nodes are already running at the specified limits.

Integrations

• Pod Autoscaler can be effected using the chaos library: litmus
• The desired chaos library can be selected by setting litmus as value for the env variable LIB

Steps to Execute the Chaos Experiment

• This Chaos Experiment can be triggered by creating a ChaosEngine resource on the cluster. To understand the values to provide in a ChaosEngine specification, refer Getting Started

• Follow the steps in the sections below to create the chaosServiceAccount, prepare the ChaosEngine & execute the experiment.

Prepare chaosServiceAccount

• Use this sample RBAC manifest to create a chaosServiceAccount in the desired (app) namespace. This example consists of the minimum necessary role permissions to execute the experiment.

Sample Rbac Manifest

---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: pod-autoscaler-sa
  namespace: default
  labels:
    name: pod-autoscaler-sa
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRole
metadata:
  name: pod-autoscaler-sa
  labels:
    name: pod-autoscaler-sa
rules:
  - apiGroups: ["", "litmuschaos.io", "batch", "apps"]
    resources:
      [
        "pods",
        "deployments",
        "jobs",
        "events",
        "chaosengines",
        "pods/log",
        "chaosexperiments",
        "chaosresults",
      ]
    verbs: ["create", "list", "get", "patch", "update", "delete"]
  - apiGroups: [""]
    resources: ["nodes"]
    verbs: ["get", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
  name: pod-autoscaler-sa
  labels:
    name: pod-autoscaler-sa
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: pod-autoscaler-sa
subjects:
  - kind: ServiceAccount
    name: pod-autoscaler-sa
    namespace: default

Prepare ChaosEngine

• Provide the application info in spec.appinfo
• Provide the auxiliary applications info (ns & labels) in spec.auxiliaryAppInfo
• Override the experiment tunables if desired in experiments.spec.components.env
• To understand the values to provided in a ChaosEngine specification, refer ChaosEngine Concepts

Supported Experiment Tunables

Variables	Description	Specify In ChaosEngine	Notes
REPLICA_COUNT	Number of replicas upto which we want to scale	Mandatory	nil
TOTAL_CHAOS_DURATION	The timeout for the chaos experiment (in seconds)	Optional	Defaults to 60
LIB	The chaos lib used to inject the chaos	Optional	Defaults to `litmus`
RAMP_TIME	Period to wait before and after injection of chaos in sec	Optional
INSTANCE_ID	A user-defined string that holds metadata/info about current run/instance of chaos. Ex: 04-05-2020-9-00. This string is appended as suffix in the chaosresult CR name.	Optional	Ensure that the overall length of the chaosresult CR is still < 64 characters

Sample ChaosEngine Manifest

apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: nginx-chaos
  namespace: default
spec:
  # It can be true/false
  annotationCheck: "false"
  # It can be active/stop
  engineState: "active"
  #ex. values: ns1:name=percona,ns2:run=nginx
  auxiliaryAppInfo: ""
  appinfo:
    appns: "default"
    applabel: "app=nginx"
    appkind: "deployment"
  chaosServiceAccount: pod-autoscaler-sa
  monitoring: false
  # It can be delete/retain
  jobCleanUpPolicy: "delete"
  experiments:
    - name: pod-autoscaler
      spec:
        components:
          env:
            # set chaos duration (in sec) as desired
            - name: TOTAL_CHAOS_DURATION
              value: "60"

            # number of replicas to scale
            - name: REPLICA_COUNT
              value: "5"

Create the ChaosEngine Resource

• Create the ChaosEngine manifest prepared in the previous step to trigger the Chaos.

  kubectl apply -f chaosengine.yml

• If the chaos experiment is not executed, refer to the troubleshooting section to identify the root cause and fix the issues.

Watch Chaos progress

• Setting up a watch of the number of repicas scaling and its state in the Kubernetes Cluster

  watch kubectl get pods -n <namespace>

Check Chaos Experiment Result

• Check whether the nodes can accomodate the application pods in the given timeout(Total Chaos Duration) , once the experiment (job) is completed. The ChaosResult resource name is derived like this: <ChaosEngine-Name>-<ChaosExperiment-Name>.

  kubectl describe chaosresult nginx-chaos-pod-autoscaler -n <application-namespace>

Pod Autoscaler Experiment Demo

• A sample recording of this experiment execution will be provided soon.