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Node Drain Experiment Details

Experiment Metadata

Type Description Tested K8s Platform
Generic Drain the node where application pod is scheduled. GKE, AWS, Packet(Kubeadm), Konvoy(AWS), EKS, 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 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 TARGET_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 does an uncordon of 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
    app.kubernetes.io/part-of: litmus
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: node-drain-sa
  labels:
    name: node-drain-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","pods/eviction"]
  verbs: ["list","get","create"]
- apiGroups: ["batch"]
  resources: ["jobs"]
  verbs: ["create","list","get","delete","deletecollection"]
- apiGroups: ["apps"]
  resources: ["daemonsets"]
  verbs: ["list","get","delete"]
- apiGroups: ["litmuschaos.io"]
  resources: ["chaosengines","chaosexperiments","chaosresults"]
  verbs: ["create","list","get","patch","update"]
- apiGroups: [""]
  resources: ["nodes"]
  verbs: ["patch","get","list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: node-drain-sa
  labels:
    name: node-drain-sa
    app.kubernetes.io/part-of: litmus
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: node-drain-sa
subjects:
- kind: ServiceAccount
  name: node-drain-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. It is an optional parameter for infra level experiment.
  • 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
TARGET_NODE Name of the node to drain Mandatory
NODE_LABEL It contains node label, which will be used to filter the target nodes if TARGET_NODE ENV is not set Optional
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 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 active/stop
  engineState: 'active'
  #ex. values: ns1:name=percona,ns2:run=nginx 
  auxiliaryAppInfo: ''
  chaosServiceAccount: node-drain-sa
  experiments:
    - name: node-drain
      spec:
        components:
        # nodeSelector: 
        #   # provide the node labels
        #   kubernetes.io/hostname: 'node02'        
          env:
            - name: TOTAL_CHAOS_DURATION
              value: '60'
              
            # enter the target node name
            - name: TARGET_NODE
              value: ''

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

  • 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>

Post Chaos Steps

  • In the beginning of experiment, we cordon the node so that chaos-pod won't schedule on the same node to which we are going to drained. The experiment itself uncordon the node in it's remedy/cleanup section. In case, experiment fails you can manually uncordon the application node using following commands:

    kubectl uncordon <node-name>

Node Drain Experiment Demo

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