Pod DNS error

Introduction

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.

Use cases

Pod DNS error:

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

note

• Kubernetes > 1.16 is required to execute this fault.
• The application pods should be in the running state before and after injecting chaos.

Fault tunables

Optional tunables

Tunable	Description	Notes
TARGET_CONTAINER	Name of the container subject to DNS error.	None. For more information, go to target specific container
TOTAL_CHAOS_DURATION	Duration for which to insert chaos (in seconds).	Default: 60 s. For more information, go to duration of the chaos
TARGET_HOSTNAMES	List of the target host names or keywords. For example, '["litmuschaos","chaosnative.com"]'.	If this is not provided, all host names/domains become the target. For more information, go to target host names
MATCH_SCHEME	Determines whether the DNS query exactly matches one of the targets or uses any of the targets as a substring. It can be exact or substring.	If this is not provided, it is set to exact. For more information, go to match scheme
PODS_AFFECTED_PERC	Percentage of total pods to target. Provide numeric values.	Default: 0 (corresponds to 1 replica). For more information, go to pod affected percentage
CONTAINER_RUNTIME	Container runtime interface for the cluster.	Default: containerd. Supports docker, containerd and crio. For more information, go to container runtime
SOCKET_PATH	Path of the docker socket file.	Default: /run/containerd/containerd.sock. For more information, go to socket path
RAMP_TIME	Period to wait before and after injecting chaos (in seconds).	For example, 30 s. For more information, go to ramp time
SEQUENCE	Sequence of chaos execution for multiple target pods.	Default: parallel. Supports serial and parallel. For more information, go to sequence of chaos execution

Target host names

Comma-separated names of the target hosts. If TARGET_HOSTNAMES is not provided, all host names or domains will be targeted. Tune it by using the TARGET_HOSTNAMES environment variable.

The following YAML snippet illustrates the use of this environment variable:

# 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

Specifies whether the DNS query should exactly match one of the targets or can have any of the targets as a substring. It supports exact or substring values. Tune it by using the MATCH_SCHEME environment variable.

The following YAML snippet illustrates the use of this environment variable:

# 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

The CONTAINER_RUNTIME and SOCKET_PATH environment variables to set the container runtime and socket file path, respectively.

• 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.

The following YAML snippet illustrates the use of these environment variables:

## 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'