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title
Simulate DNS Faults

import PickHelmVersion from '@site/src/components/PickHelmVersion'

This document describes how to create DNSChaos experiments in Chaos Mesh to simulate DNS faults.

:::info

To simulate DNS faults, you need to deploy a special DNS service called Chaos DNS Server.

After v2.6, Chaos Mesh will deploy Chaos DNS Server by default. If you don't need to simulate DNS faults, you can set dnsServer.create to false when installing Chaos Mesh:

{helm install chaos-mesh chaos-mesh/chaos-mesh --namespace=chaos-mesh --version latest --set dnsServer.create=false}

:::

DNSChaos Introduction

DNSChaos is used to simulate wrong DNS responses. For example, DNSChaos can return an error or return a random IP address when receiving a DNS request.

Check if Chaos DNS Server is deployed

Check if Chaos DNS Server is deployed by running the following command:

kubectl get pods -n chaos-mesh -l app.kubernetes.io/component=chaos-dns-server

Make sure that the Pod status is Running.

Notes

Currently, DNSChaos only supports record types A and AAAA.
The chaos DNS service runs CoreDNS with the k8s_dns_chaos plugin. If the CoreDNS service in your Kubernetes cluster contains some special configurations, you can edit configMap dns-server-config to make the configuration of the chaos DNS service consistent with that of the K8s CoreDNS service using the following command:
```
kubectl edit configmap dns-server-config -n chaos-mesh
```

Create experiments using Chaos Dashboard

Open Chaos Dashboard, and click NEW EXPERIMENT on the page to create a new experiment:
In the Choose a Target area, choose DNS FAULT and select a specific behavior, such as ERROR. Then fill out the matching rules.

According to the matching rules configured in the screenshot, the DNS FAULT takes effect for domains including google.com, chaos-mesh.org, and github.com, which means that an error will be returned when a DNS request is sent to these three domains. For details of specific matching rules, refer to the description of the patterns field in Configuration Description.
Fill out the experiment information, and specify the experiment scope and the scheduled experiment duration:
Submit the experiment information.

Create experiments using the YAML file

Write the experiment configuration to the dnschaos.yaml file:
```
apiVersion: chaos-mesh.org/v1alpha1
kind: DNSChaos
metadata:
  name: dns-chaos-example
  namespace: chaos-mesh
spec:
  action: random
  mode: all
  patterns:
    - google.com
    - chaos-mesh.*
    - github.?om
  selector:
    namespaces:
      - busybox
```
This configuration can take effect for domains including google.com, chaos-mesh.org, and github.com, which means that an IP address will be returned when a DNS request is sent to these three domains. For specific matching rules, refer to the patterns description in Configuration Description.
After the configuration file is prepared, use kubectl to create an experiment:
```
kubectl apply -f dnschaos.yaml
```

Configuration Description

Parameter	Type	Description	Default value	Required	Example
`action`	string	Defines the behavior of DNS fault. Optional values: `random` or `error`. When the value is `random`, DNS service returns a random IP address; when the value is `error`, DNS service returns an error.	None	Yes	`random` or `error`
`patterns`	String array	Selects a domain template that matches faults. Placeholder `?` and wildcard are supported. `*`	[]	No	`google.com`, `chaos-mesh.org`, `github.com`
`mode`	string	Specifies the mode of the experiment. The mode options include `one` (selecting a random Pod), `all` (selecting all eligible Pods), `fixed` (selecting a specified number of eligible Pods), `fixed-percent` (selecting a specified percentage of Pods from the eligible Pods), and `random-max-percent` (selecting the maximum percentage of Pods from the eligible Pods).	None	Yes	`one`
`value`	string	Provides parameters for the `mode` configuration, depending on `mode`. For example, when `mode` is set to `fixed-percent`, `value` specifies the percentage of Pods.	None	No	`1`
`selector`	struct	Specifies the target Pod. For details, refer to Define the Scope of Chaos Experiments.	None	Yes

:::note

The wildcard in patterns configuration must be at the end of string. For example, chaos-mes*.org. is an invalid configuration.
When patterns is not configured, faults are injected for all domains.

:::

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