litmus-docs/website/versioned_docs/version-1.4.0/node-drain.md

id	title	sidebar_label	original_id
node-drain	Node Drain Experiment Details	Node Drain	node-drain

---

Experiment Metadata

Type	Description	Tested K8s Platform
Generic	Drain the node where application pod is scheduled.	GKE, AWS, Packet(Kubeadm), Konvoy(AWS), EKS

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 node-drain experiment resource is available in the cluster by executing kubectl get chaosexperiments in the desired namespace. If not, install from here

• Ensure that the node specified in the experiment ENV variable APP_NODE (the node which will be drained) should be cordoned before execution of the chaos experiment (before applying the chaosengine manifest) to ensure that the litmus experiment runner pods are not scheduled on it / subjected to eviction. This can be achieved with the following steps:

  • Get node names against the applications pods: kubectl get pods -o wide
  • Cordon the node kubectl cordon <nodename>

Entry Criteria

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

Exit Criteria

• Target nodes are in Ready state post chaos injection

Details

• This experiment drains the node where application pod is running and verifies if it is scheduled on another available node.
• In the end of experiment it uncordons the specified node so that it can be utilised in future.

Integrations

• Drain node 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 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: node-drain-sa
  namespace: default
  labels:
    name: node-drain-sa
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRole
metadata:
  name: node-drain-sa
  labels:
    name: node-drain-sa
rules:
  - apiGroups: ["", "litmuschaos.io", "batch", "extensions"]
    resources:
      [
        "pods",
        "jobs",
        "events",
        "chaosengines",
        "pods/log",
        "daemonsets",
        "pods/eviction",
        "chaosexperiments",
        "chaosresults",
      ]
    verbs: ["create", "list", "get", "patch", "update", "delete"]
  - apiGroups: [""]
    resources: ["nodes"]
    verbs: ["patch", "get", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
  name: node-drain-sa
  labels:
    name: node-drain-sa
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: node-drain-sa
subjects:
  - kind: ServiceAccount
    name: node-drain-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
APP_NODE	Name of the node to drain	Mandatory
TOTAL_CHAOS_DURATION	The time duration for chaos insertion (seconds)	Optional	Defaults to 60s
LIB	The chaos lib used to inject the chaos	Optional	Defaults to `litmus`
RAMP_TIME	Period to wait before 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: node-drain-sa
  monitoring: false
  # It can be delete/retain
  jobCleanUpPolicy: "delete"
  experiments:
    - name: node-drain
      spec:
        components:
          env:
            # set node name
            - name: APP_NODE
              value: "node-1"

Create the ChaosEngine Resource

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

  kubectl apply -f chaosengine.yml

Watch Chaos progress

• Set up a watch on the applications originally scheduled on the affected node and verify whether they are rescheduled on the other nodes in the Kubernetes Cluster.

  watch kubectl get pods,nodes --all-namespaces

Check Chaos Experiment Result

• Check whether the application is resilient to the node drain, once the experiment (job) is completed. The ChaosResult resource name is derived like this: <ChaosEngine-Name>-<ChaosExperiment-Name>.

  kubectl describe chaosresult nginx-chaos-node-drain -n <application-namespace>

Node Drain Experiment Demo [TODO]

• A sample recording of this experiment execution is provided here.