Pod DNS error

Pod DNS error is a Kubernetes pod-level chaos fault that injects chaos to disrupt DNS resolution in pods.

• It removes access to services by blocking the DNS resolution of host names (or domains).

Usage

View fault usage

This fault determines the resilience of an application to DNS errors. It determines how quickly an application can resolve the host names and recover from the failure. It simulates unavailability of DNS server (loss of access to any external domain from a given microservice) and malfunctioning of DNS server (loss of access to specific domains from a given microservice, access to cloud provider dependencies, and access to specific third party services).

Prerequisites

• Kubernetes> 1.16.

Default validations

The application pods should be in running state before and after chaos injection.

Fault tunables

Fault tunables

Optional fields

Variables	Description	s
TARGET_CONTAINER	Name of container which is subjected to dns-error	None
TOTAL_CHAOS_DURATION	The time duration for chaos insertion (seconds)	Default (60s)
TARGET_HOSTNAMES	List of the target hostnames or keywords For example, '["litmuschaos","chaosnative.com"]'	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	if not provided, it will be set as exact
PODS_AFFECTED_PERC	The Percentage of total pods to target	Defaults to 0 (corresponds to 1 replica), provide numeric value only
CONTAINER_RUNTIME	container runtime interface for the cluster	Defaults to containerd, supported values: docker, containerd and crio
SOCKET_PATH	Path of the docker socket file	Defaults to /run/containerd/containerd.sock
LIB_IMAGE	Image used to run the netem command	Defaults to litmuschaos/go-runner:latest
RAMP_TIME	Period to wait before and after injection of chaos in sec	For example, 30
SEQUENCE	It defines sequence of chaos execution for multiple target pods	Default value: parallel. Supported: serial, parallel

Fault examples

Common and pod-specific tunables

Refer to the common attributes and pod-specific tunables to tune the common tunables for all fault and pod specific tunables.

Target Host Names

It defines the comma-separated name of the target hosts subjected to chaos. It can be tuned with the TARGET_HOSTNAMES ENV. If TARGET_HOSTNAMESnot provided then all hostnames/domains will be targeted.

Use the following example to tune it:

# contains the target host names for the dns error
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  annotationCheck: "false"
  appinfo:
    appns: "default"
    applabel: "app=nginx"
    appkind: "deployment"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: pod-dns-error
    spec:
      components:
        env:
        ## comma separated list of host names
        ## if not provided, all hostnames/domains will be targeted
        - name: TARGET_HOSTNAMES
          value: '["litmuschaos","chaosnative.com"]'
        - name: TOTAL_CHAOS_DURATION
          value: '60'

Match Scheme

It determines whether the DNS query has to match exactly with one of the targets or can have any of the targets as a substring. It can be tuned with MATCH_SCHEME ENV. It supports exact or substring values.

Use the following example to tune it:

# contains match scheme for the dns error
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  annotationCheck: "false"
  appinfo:
    appns: "default"
    applabel: "app=nginx"
    appkind: "deployment"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: pod-dns-error
    spec:
      components:
        env:
        ## it supports 'exact' and 'substring' values
        - name: MATCH_SCHEME
          value: 'exact' 
        - name: TOTAL_CHAOS_DURATION
          value: '60'

Container runtime and socket path

It defines the CONTAINER_RUNTIME and SOCKET_PATH ENV to set the container runtime and socket file path.

• CONTAINER_RUNTIME: It supports docker, containerd, and crio runtimes. The default value is containerd.
• SOCKET_PATH: It contains path of containerd socket file by default(/run/containerd/containerd.sock). For docker, specify path as /var/run/docker.sock. For crio, specify path as /var/run/crio/crio.sock.

Use the following example to tune it:

## provide the container runtime and socket file path
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: engine-nginx
spec:
  engineState: "active"
  annotationCheck: "false"
  appinfo:
    appns: "default"
    applabel: "app=nginx"
    appkind: "deployment"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: pod-dns-error
    spec:
      components:
        env:
        # runtime for the container
        # supports docker
        - name: CONTAINER_RUNTIME
          value: 'containerd'
        # path of the socket file
        - name: SOCKET_PATH
          value: '/run/containerd/containerd.sock'
        - name: TOTAL_CHAOS_DURATION
          VALUE: '60'