Container Compute Service:Add annotations to configure a custom DNS server

Scenarios

In the following scenarios, you can add annotations to configure a custom DNS server:

• Scenario 1: You want to use the Default DNS policy use acs-profile to customize the DNS service for the entire ACS cluster.

• Scenario 2: You want to use the ClusterFirst DNS policy and use a self-managed DNS server to resolve the domain name of the image repository.

• Scenario 3: You want to use the Default DNS policy and use acs-profile to customize the DNS service for the entire ACS cluster. In addition, you want to use a self-managed DNS server to resolve the domain name of the image repository.

This method is not applicable to the following scenarios:

• You want to use a DNS server provided by Alibaba Cloud DNS to resolve the domain names of applications and the image repository. In this case, we recommend that you use the Default DNS policy. Do not use custom DNS servers.

• You want to use a self-managed DNS service to resolve the domain names of applications and use a DNS server provided by Alibaba Cloud DNS to resolve the domain name of the image repository. In this case, we recommend that you use the None DNS policy and set the dnsConfig field in the pod spec to specify the self-managed DNS server. For more information, see Scenario 2: Customize DNS settings for a pod.

Configuration introduction

You can add the network.alibabacloud.com/custom-dnsconfig annotation to the metadata in the configuration file of a pod to use a custom DNS server. The value of this annotation is in the {"servers":["20.1.xx.xx","30.1.xx.xx"],"searches":["xx.com","yy.com"],"options":["ndots:2","edns0"]} format, which is a standard Kubernetes spec.dnsConfig structure.

The following section shows the configuration.

{
    "servers": [
        "20.1.xx.xx",
        "30.1.xx.xx"
    ],
    "searches": [
        "xx.com",
        "yy.com"
    ],
    "options": [
        "ndots:2",
        "edns0"
    ]
}

The following table describes the fields.

Procedure

The following example uses a stateless application:

1. Create a file named deploy.yaml and add the following content to the file:

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     labels:
       app: test
     name: test-default
   spec:
     replicas: 1
     selector:
       matchLabels:
         app: test
     template:
       metadata:
         annotations:
           network.alibabacloud.com/custom-dnsconfig: '{"servers":["20.1.XXX.XXX","30.1.X.X"],"searches":["xx.com","yy.com"],"options":["ndots:2","edns0"]}'
         labels:
           app: test
       spec:
         containers:
         - image: registry.cn-hangzhou.aliyuncs.com/acs/busybox:v1.29.2
           command: ["sh","-c","i=1; while true; do echo $i; i=$((i=i+1)); sleep 1; done;"]
           name: busybox
           resources:
             requests:
               cpu: "2"
               memory: "8Gi"
             limits:
               cpu: "2"
               memory: "8Gi"
         dnsPolicy: Default

2. Deploy the application.

   kubectl apply -f deploy.yaml

3. Check the result.

   kubectl  exec  <pod name>  cat /etc/resolv.conf

   Expected results:

   search xx.com yy.com
   nameserver 20.1.XXX.XXX
   nameserver 30.1.XXX.XXX
   nameserver 100.100.2.136
   options ndots:6 edns

Cluster configuration

You can configure pod auto injection in the acs-profile to customize DNS resolution for the entire cluster. The following code block shows the content of the acs-profile that automatically injects custom DNS configurations into all pods in the default namespace. After you apply the acs-profile, you no longer need to add pod annotations. You need only to set dnsPolicy to Default. For more information about the acs-profile, see Configure an acs-profile to automatically inject pod configurations.

apiVersion: v1
kind: ConfigMap
metadata:
  name: acs-profile
  namespace: kube-system
data:
  selectors: |
    [
      {
        "name": "selector-demo1",
        "namespaceSelector": {
          "matchLabels": {
            "kubernetes.io/metadata.name": "default"
          }
        },
        "effect": {
          "annotations": {
            "network.alibabacloud.com/custom-dnsconfig": "{\"servers\":[\"20.1.XXX.XXX\",\"30.1.X.X\"],\"searches\":[\"xx.com\",\"yy.com\"],\"options\":[\"ndots:2\",\"edns0\"]}"
          }
        }
      }
    ]