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OpenEBS Pool Container Failure Experiment Details

Experiment Metadata

Type Description Tested K8s Platform
OpenEBS Kill the cstor pool pod container and check if gets created again GKE, EKS, Konvoy(AWS), Packet(Kubeadm), Minikube, OpenShift(Baremetal)
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: In this example, we are using nginx as stateful application that stores static pages on a Kubernetes volume.

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 openebs-pool-container-failure experiment resource is available in the cluster. If not, install from here

  • The DATA_PERSISTENCE can be enabled by provide the application's info in a configmap volume so that the experiment can perform necessary checks. Currently, LitmusChaos supports data consistency checks only for MySQL and Busybox.

    • For MYSQL data persistence check create a configmap as shown below in the application namespace (replace with actual credentials):
    ---
apiVersion: v1
kind: ConfigMap
metadata:
  name: openebs-pool-container-failure
data:
  parameters.yml: | 
    dbuser: root
    dbpassword: k8sDem0
    dbname: test
    • For Busybox data persistence check create a configmap as shown below in the application namespace (replace with actual credentials):
    ---
apiVersion: v1
kind: ConfigMap
metadata:
  name: openebs-pool-container-failure
data:
  parameters.yml: | 
    blocksize: 4k
    blockcount: 1024
    testfile: exampleFile

  • Ensure that the chaosServiceAccount used for the experiment has cluster-scope permissions as the experiment may involve carrying out the chaos in the openebs namespace while performing application health checks in its respective namespace.

  • Ensure that you have adequate amount of CPU and Memory resources available in your cluster to run the experiment.

Entry Criteria

  • Application pods are healthy before chaos injection
  • Application writes are successful on OpenEBS PVs

Exit Criteria

  • Stateful application pods are healthy post chaos injection
  • OpenEBS Storage target pods are healthy

If the experiment tunable DATA_PERSISTENCE is set to 'enabled':

  • Application data written prior to chaos is successfully retrieved/read
  • Database consistency is maintained as per db integrity check utils

Details

  • This scenario validates the behaviour of stateful applications and OpenEBS data plane upon forced termination of the targeted pool pod container
  • Containers are killed using the kill command provided by pumba
  • Pumba is run as a daemonset on all nodes in dry-run mode to begin with; the kill command is issued during experiment execution via kubectl exec
  • Can test the stateful application's resilience to momentary iSCSI connection loss

Integrations

  • Container kill is achieved using the pumba chaos library for docker runtime.
  • The desired lib image can be configured in the env variable LIB_IMAGE.

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 be provided 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 cluster role permissions to execute the experiment.

Sample Rbac Manifest

---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: pool-container-failure-sa
  namespace: default
  labels:
    name: pool-container-failure-sa
    app.kubernetes.io/part-of: litmus
---
# Source: openebs/templates/clusterrole.yaml
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: pool-container-failure-sa
  labels:
    name: pool-container-failure-sa
    app.kubernetes.io/part-of: litmus
rules:
- apiGroups: ["","apps","litmuschaos.io","batch","extensions","storage.k8s.io","openebs.io"]
  resources: ["pods","jobs","events","pods/log","replicasets","pods/exec","configmaps","secrets","persistentvolumeclaims","cstorvolumereplicas","chaosexperiments","chaosresults","chaosengines"]
  verbs: ["create","list","get","patch","update","delete"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: pool-container-failure-sa
  labels:
    name: pool-container-failure-sa
    app.kubernetes.io/part-of: litmus
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: pool-container-failure-sa
subjects:
- kind: ServiceAccount
  name: pool-container-failure-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
  • Provide the configMaps and secrets in experiments.spec.components.configMaps/secrets, For more info refer Sample ChaosEngine
  • To understand the values to provided in a ChaosEngine specification, refer ChaosEngine Concepts

Supported Experiment Tunables

Variables Description Specify In ChaosEngine Notes
APP_PVC The PersistentVolumeClaim used by the stateful application Mandatory PVC must use OpenEBS cStor storage class
TOTAL_CHAOS_DURATION Amount of soak time for I/O post container kill Optional Defaults to 600 seconds
LIB_IMAGE The chaos library image used to inject the latency Optional Defaults to `gaiaadm/pumba:0.6.5`. Supported: `gaiaadm/pumba:0.6.5`
DEPLOY_TYPE Type of Kubernetes resource used by the stateful application Optional Defaults to `deployment`. Supported: `deployment`, `statefulset`
DATA_PERSISTENCE Flag to perform data consistency checks on the application Optional Default value is disabled (empty/unset). It supports only `mysql` and `busybox`. Ensure configmap with app details are created
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: pool-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: pool-container-failure-sa
  experiments:
    - name: openebs-pool-container-failure
      spec:
        components:
          env:
            # provide the total chaos duration
            - name: TOTAL_CHAOS_DURATION
              value: '20'

            - name: APP_PVC
              value: 'demo-nginx-claim'   
               
            - name: DEPLOY_TYPE
              value: 'deployment'

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 pod restart count by setting up a watch on the pods in the OpenEBS namespace

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

Check Chaos Experiment Result

  • Check whether the application is resilient to the pool pod container failure, once the experiment (job) is completed. The ChaosResult resource naming convention is: <ChaosEngine-Name>-<ChaosExperiment-Name>.

    kubectl describe chaosresult target-chaos-openebs-pool-container-failure -n <application-namespace>

OpenEBS Pool Container Failure Demo [TODO]

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