pod-dns-error.md

id	title	sidebar_label
pod-dns-error	Pod DNS Error Experiment Details	Pod DNS Error

---

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>