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Pod DNS Error Experiment Details

Experiment Metadata

Type Description Tested K8s Platform
Generic Injects dns failure/error in target pods EKS, Minikube > v1.6.0

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 pod-dns-error 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 before chaos injection

Exit Criteria

  • Application pods are healthy post chaos injection

Details

  • Pod-dns-error injects chaos to disrupt dns resolution in kubernetes pods.
  • The application pod should be healthy once chaos is stopped.
  • Causes loss of access to services by blocking dns resolution of hostnames/domains

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: pod-dns-error-sa
  namespace: default
  labels:
    name: pod-dns-error-sa
    app.kubernetes.io/part-of: litmus
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: pod-dns-error-sa
  namespace: default
  labels:
    name: pod-dns-error-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", "replicationcontrollers"]
    verbs: ["create", "list", "get"]
  - apiGroups: ["batch"]
    resources: ["jobs"]
    verbs: ["create", "list", "get", "delete", "deletecollection"]
  - apiGroups: ["apps"]
    resources: ["deployments", "statefulsets", "daemonsets", "replicasets"]
    verbs: ["list", "get"]
  - apiGroups: ["apps.openshift.io"]
    resources: ["deploymentconfigs"]
    verbs: ["list", "get"]
  - apiGroups: ["argoproj.io"]
    resources: ["rollouts"]
    verbs: ["list", "get"]
  - apiGroups: ["litmuschaos.io"]
    resources: ["chaosengines", "chaosexperiments", "chaosresults"]
    verbs: ["create", "list", "get", "patch", "update"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: pod-dns-error-sa
  namespace: default
  labels:
    name: pod-dns-error-sa
    app.kubernetes.io/part-of: litmus
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: pod-dns-error-sa
subjects:
  - kind: ServiceAccount
    name: pod-dns-error-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
  • 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_CONTAINER Name of container which is subjected to dns-error Optional None
TOTAL_CHAOS_DURATION The time duration for chaos insertion (seconds) Optional Default (60s)
TARGET_HOSTNAMES List of the target hostnames or keywords eg. '["litmuschaos","chaosnative.com"]' Optional If not provided, all hostnames/domains will be targeted
MATCH_SCHEME Determines whether the dns query has to match exactly with one of the targets or can have any of the targets as substring. Can be either exact or substring Optional if not provided, it will be set as exact
PODS_AFFECTED_PERC The Percentage of total pods to target Optional Defaults to 0 (corresponds to 1 replica), provide numeric value only
CONTAINER_RUNTIME container runtime interface for the cluster Optional Defaults to docker, supported values: docker
SOCKET_PATH Path of the docker socket file Optional Defaults to `/var/run/docker.sock`
LIB The chaos lib used to inject the chaos Optional Default value: litmus, supported values: litmus
LIB_IMAGE Image used to run the netem command Optional Defaults to `litmuschaos/go-runner:latest`
RAMP_TIME Period to wait before and after injection of chaos in sec Optional
SEQUENCE It defines sequence of chaos execution for multiple target pods 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
spec:
  appinfo:
    appns: "default"
    applabel: "app=nginx"
    appkind: "deployment"
  # It can be active/stop
  engineState: "active"
  #ex. values: ns1:name=percona,ns2:run=nginx
  auxiliaryAppInfo: ""
  chaosServiceAccount: pod-dns-error-sa
  experiments:
    - name: pod-dns-error
      spec:
        components:
          env:
            - name: TOTAL_CHAOS_DURATION
              value: "60" # in seconds

            # list of the target hostnames or kewywords eg. '["litmuschaos","chaosnative.io"]' . If empty all hostnames are targets
            - name: TARGET_HOSTNAMES
              value: ""

            # can be either exact or substring, determines whether the dns query has to match exactly with one of the targets or can have any of the targets as substring
            - name: MATCH_SCHEME
              value: "exact"

            # provide the name of container runtime, it supports docker, containerd, crio
            - name: CONTAINER_RUNTIME
              value: "docker"

            # provide the socket file path
            - name: SOCKET_PATH
              value: "/var/run/docker.sock"

             ## percentage of total pods to target
            - name: PODS_AFFECTED_PERC
              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 dns failure by setting up a ping on the target domain/hostname from the affected pod, should error out.

    ping <target_domain>

Abort/Restart the Chaos Experiment

  • To stop the pod-dns-error 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 Pod Dns Chaos, once the experiment (job) is completed. The ChaosResult resource name is derived like this: <ChaosEngine-Name>-<ChaosExperiment-Name>.

    kubectl describe chaosresult <ChaosEngine-Name>-<ChaosExperiment-Name> -n <application-namespace>

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