Node Restart Experiment Details

Experiment Metadata

Type	Description	Tested K8s Platform
Generic	Restart the target node	Kubevirt VMs, AWS(kubeadm), EKS

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-restart experiment resource is available in the cluster by executing kubectl get chaosexperiments in the desired namespace. If not, install from here
Create a Kubernetes secret named id-rsa where the experiment will run, where its contents will be the private SSH key for SSH_USER used to connect to the node that hosts the target pod in the secret field ssh-privatekey. A sample secret is shown below:

apiVersion: v1
kind: Secret
metadata:
  name: id-rsa
type: kubernetes.io/ssh-auth
stringData:
  ssh-privatekey: |-
    # SSH private key for ssh contained here

Creating the RSA key pair for remote SSH access should be a trivial exercise for those who are already familiar with an ssh client, which entails the following actions:

Create a new key pair and store the keys in a file named my-id-rsa-key and my-id-rsa-key.pub for the private and public keys respectively:

ssh-keygen -f ~/my-id-rsa-key -t rsa -b 4096

For each node available, run this following command to copy the public key of my-id-rsa-key:

ssh-copy-id -i my-id-rsa-key user@node

For further details, please check this documentation. Once you have copied the public key to all nodes and created the secret described earlier, you are ready to start your experiment.

Entry-Criteria

Application pods should be healthy before chaos injection.
Target Nodes should be in Ready state before chaos injection.

Exit-Criteria

Application pods should be healthy after chaos injection.
Target Nodes should be in Ready state after chaos injection.

Details

Causes chaos to disrupt state of node by restarting it.
Tests deployment sanity (replica availability & uninterrupted service) and recovery workflows of the application pod

Integrations

Node Restart can be effected using the chaos library: litmus.

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: node-restart-sa
  namespace: default
  labels:
    name: node-restart-sa
    app.kubernetes.io/part-of: litmus
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: node-restart-sa
  labels:
    name: node-restart-sa
    app.kubernetes.io/part-of: litmus
rules:
- apiGroups: [""]
  resources: ["pods","events","secrets"]
  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: ["litmuschaos.io"]
  resources: ["chaosengines","chaosexperiments","chaosresults"]
  verbs: ["create","list","get","patch","update"]
- apiGroups: [""]
  resources: ["nodes"]
  verbs: ["get","list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: node-restart-sa
  labels:
    name: node-restart-sa
    app.kubernetes.io/part-of: litmus
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: node-restart-sa
subjects:
- kind: ServiceAccount
  name: node-restart-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.
Populate the TARGET_NODE and TARGET_NODE_IP in the experiments.spec.components.env section. Note that the environment values take precedence over the spec.appinfo fields.
Provide the auxiliary applications info (ns & labels) in spec.auxiliaryAppInfo
Override the extra 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
LIB_IMAGE	The image used to restart the node	Optional	Defaults to `litmuschaos/go-runner:latest`
SSH_USER	name of ssh user	Mandatory	Defaults to `root`
TARGET_NODE	Name of target node, subjected to chaos. If not provided, the experiment will lookup the node that hosts the pod running based on the `appInfo` details section in the `ChaosEngine`. If provided, it also requires the `TARGET_NODE_IP` to be populated.	Optional	Defaults to empty
NODE_LABEL	It contains node label, which will be used to filter the target nodes if TARGET_NODE ENV is not set	Optional
TARGET_NODE_IP	Internal IP of the target node, subjected to chaos. If not provided, the experiment will lookup the node IP that hosts the pod running based on the `appInfo` details section in the `ChaosEngine`. If provided, it also requires `TARGET_NODE` to be populated.	Optional	Defaults to empty
REBOOT_COMMAND	Command used for reboot	Mandatory	Defaults to `sudo systemctl reboot`
TOTAL_CHAOS_DURATION	The time duration for chaos insertion (sec)	Optional	Defaults to 30s
RAMP_TIME	Period to wait before and after injection of chaos in sec	Optional
LIB	The chaos lib used to inject the chaos	Optional	Defaults to `litmus` supported litmus only
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-restart-sa
  experiments:
    - name: node-restart
      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: ''

            # ENTER THE TARGET NODE IP
            - name: TARGET_NODE_IP
              value: ''

             # ENTER THE USER TO BE USED FOR SSH AUTH
            - name: SSH_USER
              value: 'root'

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

SSH into the targeted node and verify the uptime. The uptime should be reinitialized to 0mins after the node restart.

root@<node-name>$ uptime

Check Chaos Experiment Result

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

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

Node Restart Experiment Demo

A sample recording of this experiment execution will be added soon.

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