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OpenEBS Pool Network Loss Experiment Details

Experiment Metadata

Type Description Tested K8s Platform
OpenEBS Induce network loss into the cStor pool pod GKE, EKS

Note: In this example, we are using nginx as stateful application that stores static pages on a Kubernetes volume.

Prerequisites

  • Ensure that the Kubernetes Cluster uses Docker runtime

  • 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-network-loss experiment resource is available in the cluster by executing kubectl get chaosexperiments in the specificed namespace. 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-network-loss
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-network-loss
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.

Entry Criteria

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

Exit Criteria

  • Application pods are healthy post chaos injection
  • OpenEBS Storage pool pods are healthy

If the experiment tunable DATA_PERSISTENCE is set to 'mysql' or 'busybox':

  • 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 high latencies/network loss in accessing the storage replicas pod
  • Injects network loss on the specified container in the controller pod by starting a traffic control tc process with netem rules to add packet loss
  • Network loss is injected via pumba library with command pumba netem loss by passing the relevant network interface, network loss, chaos duration and regex filter for container name
  • Can test the stateful application's resilience to loss/slow iSCSI connections

Integrations

  • Network loss is achieved using the pumba chaos library in case of docker runtime. Support for other other runtimes via tc direct invocation of tc will be added soon.
  • 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 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 cluster role permissions to execute the experiment.

Sample Rbac Manifest

---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: pool-network-loss-sa
  namespace: default
  labels:
    name: pool-network-loss-sa
---
# Source: openebs/templates/clusterrole.yaml
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: pool-network-loss-sa
  labels:
    name: pool-network-loss-sa
rules:
- apiGroups: ["","apps","litmuschaos.io","batch","extensions","storage.k8s.io","openebs.io"]
  resources: ["pods","pods/exec","pods/log","events","jobs","configmaps","services","persistentvolumeclaims","storageclasses","persistentvolumes","chaosengines","chaosexperiments","chaosresults","cstorpools","cstorvolumereplicas","replicasets"]
  verbs: ["create","list","get","patch","update","delete"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: pool-network-loss-sa
  labels:
    name: pool-network-loss-sa
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: pool-network-loss-sa
subjects:
- kind: ServiceAccount
  name: pool-network-loss-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 may use either OpenEBS cStor storage class
TC_IMAGE Image used for traffic control in linux Optional default value is `gaiadocker/iproute2`
LIB_IMAGE chaos library image used to inject the network loss Optional Defaults to `gaiaadm/pumba:0.6.5`. Supported: `docker : gaiaadm/pumba:0.6.5`
TOTAL_CHAOS_DURATION Total duration for which network loss is injected Optional Defaults to 120 seconds
NETWORK_PACKET_LOSS_PERCENTAGE Total percentage for which network loss is injected Optional Defaults to 100 (percent)
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:
  auxiliaryAppInfo: ''
  # It can be active/stop
  engineState: 'active'
  appinfo:
    appns: 'default'
    applabel: 'app=nginx'
    appkind: 'deployment'
  chaosServiceAccount: pool-network-loss-sa
  experiments:
    - name: openebs-pool-network-loss
      spec:
        components:
          env:
          - name: TOTAL_CHAOS_DURATION
            value: '120' # in seconds

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

          - name: NETWORK_PACKET_LOSS_PERCENTAGE
            value: '100'

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 network loss in action by setting up a ping to the storage controller in the OpenEBS namespace

  • Watch the behaviour of the application pod and the OpenEBS data replica/pool pods by setting up in a watch on the respective namespaces

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

Check Chaos Experiment Result

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

    kubectl describe chaosresult pool-chaos-openebs-pool-network-loss -n <application-namespace>

OpenEBS Pool Network Loss Demo [TODO]

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