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Node IO Stress Experiment Details

Experiment Metadata

Type Description Tested K8s Platform
Generic Give IO Disk Stress on the Kubernetes Node 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 node-io-stress 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 may or may not be healthy post chaos injection

Details

  • This experiment causes io stress on the Kubernetes node. The experiment aims to verify the resiliency of applications that share this disk resource for ephemeral or persistent storage purposes.
  • The amount of io stress can be either specifed as the size in percentage of the total free space on the file system or simply in Gigabytes(GB). When provided both it will execute with the utilization percentage specified and non of them are provided it will execute with default value of 10%.
  • Tests application resiliency upon replica evictions caused due IO stress on the available Disk space.

Integrations

  • Node IO Stress can be injected using the chaos library: litmus
  • This can be provided under under LIB variable

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-io-stress-sa
  namespace: default
  labels:
    name: node-io-stress-sa
    app.kubernetes.io/part-of: litmus
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: node-io-stress-sa
  labels:
    name: node-io-stress-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: ["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-io-stress-sa
  labels:
    name: node-io-stress-sa
    app.kubernetes.io/part-of: litmus
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: node-io-stress-sa
subjects:
- kind: ServiceAccount
  name: node-io-stress-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_NODES Comma separated list of nodes, subjected to node io stress Mandatory
NODE_LABEL It contains node label, which will be used to filter the target nodes if TARGET_NODES ENV is not set Optional
TOTAL_CHAOS_DURATION The time duration for chaos (seconds) Optional Default to 120
FILESYSTEM_UTILIZATION_PERCENTAGE Specify the size as percentage of free space on the file system Optional Default to 10%
FILESYSTEM_UTILIZATION_BYTES Specify the size in GigaBytes(GB). FILESYSTEM_UTILIZATION_PERCENTAGE & FILESYSTEM_UTILIZATION_BYTES are mutually exclusive. If both are provided, FILESYSTEM_UTILIZATION_PERCENTAGE is prioritized. Optional
CPU Number of core of CPU to be used Optional Default to 1
NUMBER_OF_WORKERS It is the number of IO workers involved in IO disk stress Optional Default to 4
VM_WORKERS It is the number vm workers involved in IO disk stress Optional Default to 1
LIB The chaos lib used to inject the chaos Optional Default to litmus
LIB_IMAGE Image used to run the stress command Optional Default to litmuschaos/go-runner:latest
RAMP_TIME Period to wait before and after injection of chaos in sec Optional
NODES_AFFECTED_PERC The Percentage of total nodes to target Optional Defaults to 0 (corresponds to 1 node), provide numeric value only
SEQUENCE It defines sequence of chaos execution for multiple target nodes Optional Default value: parallel. Supported: serial, parallel
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-io-stress-sa
  experiments:
    - name: node-io-stress
      spec:
        components:
          env:
            # set chaos duration (in sec) as desired
            - name: TOTAL_CHAOS_DURATION
              value: '120'

            ## specify the size as percentage of free space on the file system
            - name: FILESYSTEM_UTILIZATION_PERCENTAGE
              value: '10'

            ## Number of core of CPU
            - name: CPU
              value: '1'

            ## Total number of workers default value is 4
            - name: NUMBER_OF_WORKERS
              value: '4'                               
            
             ## percentage of total nodes to target
            - name: NODES_AFFECTED_PERC
              value: ''

            # provide the comma separated target node names
            - name: TARGET_NODES
              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

  • View the status of the pods as they are subjected to IO disk stress.

    watch -n 1 kubectl get pods -n <application-namespace>

  • Monitor the capacity filled up on the host filesystem

    watch du -h

Abort/Restart the Chaos Experiment

  • To stop the pod-io-stress experiment immediately, either delete the ChaosEngine resource or execute the following command:

    kubectl patch chaosengine <chaosengine-name> -n <namespace> --type merge --patch '{"spec":{"engineState":"stop"}}'

  • To restart the experiment, either re-apply the ChaosEngine YAML or execute the following command:

    kubectl patch chaosengine <chaosengine-name> -n <namespace> --type merge --patch '{"spec":{"engineState":"active"}}'

Check Chaos Experiment Result

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

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

Node IO Stress Experiment Demo

  • The Demo Video will be Added soon.
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