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pod-autoscaler.md

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pod-autoscaler
Scale the application replicas and test the node autoscaling on cluster
Pod Autoscaler

Experiment Metadata

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

Prerequisites

  • Ensure that Kubernetes Version > 1.16
  • 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
    app.kubernetes.io/part-of: litmus
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: pod-autoscaler-sa
  labels:
    name: pod-autoscaler-sa
    app.kubernetes.io/part-of: litmus
rules:
- apiGroups: [""]
  resources: ["pods","events"]
  verbs: ["create","list","get","patch","update","delete","deletecollection"]
- apiGroups: [""]
  resources: ["pods/exec","pods/log"]
  verbs: ["create","list","get"]
- apiGroups: ["batch"]
  resources: ["jobs"]
  verbs: ["create","list","get","delete","deletecollection"]
- apiGroups: ["apps"]
  resources: ["deployments","statefulsets"]
  verbs: ["list","get","patch","update"]
- apiGroups: ["litmuschaos.io"]
  resources: ["chaosengines","chaosexperiments","chaosresults"]
  verbs: ["create","list","get","patch","update"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: pod-autoscaler-sa
  labels:
    name: pod-autoscaler-sa
    app.kubernetes.io/part-of: litmus
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: pod-autoscaler-sa
subjects:
- kind: ServiceAccount
  name: pod-autoscaler-sa
  namespace: default

Note: In case of restricted systems/setup, create a PodSecurityPolicy(psp) with the required permissions. The chaosServiceAccount can subscribe to work around the respective limitations. An example of a standard psp that can be used for litmus chaos experiments can be found here.

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

NOTE: Provide the label of resource object (deployment/statefulset) in the appinfo section of chaosengine while running this experiment and NOT the pod label. You can check the resource object label using kubectl get <resource-type> --show-labels (where resource-type can be deploy,sts).

Sample ChaosEngine Manifest

apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: nginx-chaos
  namespace: default
spec:
  # 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
  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.