Properly Configuring CoreDNS

Configuring CoreDNS Specifications

1. Log in to the CCE console and click the cluster name to access the cluster console.
2. In the navigation pane, choose Add-ons. Then, click Edit under CoreDNS.
3. In the Specifications area, configure CoreDNS specifications.
4. Change the number of pods, CPU quotas, and memory quotas as needed to adjust the domain name resolution QPS provided by CoreDNS.

   

5. Click OK.

Properly Configuring the Stub Domain for DNS

1. Log in to the CCE console and click the cluster name to access the cluster console.
2. In the navigation pane, choose Add-ons. Then, click Edit under CoreDNS.
3. Add a stub domain in the Parameters area. The format is a key-value pair. The key is a DNS suffix domain name, and the value is a DNS IP address or a group of DNS IP addresses, for example, consul.local -- 10.150.0.1.
   Figure 1 Adding a stub domain
   
   Corefile:

   .:5353 {
       bind {$POD_IP}
       cache 30 {
           servfail 5s
       }
       errors
       health {$POD_IP}:8080
       kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           fallthrough in-addr.arpa ip6.arpa
       }
       loadbalance round_robin
       prometheus {$POD_IP}:9153
       forward . /etc/resolv.conf {
           policy random
       }
       reload
       ready {$POD_IP}:8081
   }
   consul.local:5353 {
       bind {$POD_IP}
       errors
       cache 30
       forward . 10.150.0.1
   }

4. Click OK.
5. Choose ConfigMaps and Secrets in the navigation pane, select the kube-system namespace, and view the ConfigMap data of coredns to check whether the update is successful.

Properly Configuring the Host

To specify hosts for a specific domain name, you can use the hosts add-on. An example is as follows:

1. Log in to the CCE console and click the cluster name to access the cluster console.
2. In the navigation pane, choose Add-ons. Then, click Edit under CoreDNS.
3. Edit extended parameters in Parameters and add the following content to the plugins field:

   {
     "configBlock": "192.168.1.1 www.example.com\nfallthrough",
     "name": "hosts"
   }

   

   The fallthrough field must be configured. fallthrough indicates that when the domain name to be resolved cannot be found in the hosts file, the resolution task is transferred to the next add-on of CoreDNS. If fallthrough is not specified, the task ends and the domain name resolution stops. As a result, the domain name resolution in the cluster fails.

   For details about how to configure the hosts file, visit https://coredns.io/plugins/hosts/.

   Figure 2 Modifying the CoreDNS hosts configuration
   
   Corefile:

   .:5353 {
       bind {$POD_IP}
       hosts {
         192.168.1.1 www.example.com
         fallthrough
       }
       cache 30
       errors
       health {$POD_IP}:8080
       kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           fallthrough in-addr.arpa ip6.arpa
       }
       loadbalance round_robin
       prometheus {$POD_IP}:9153
       forward . /etc/resolv.conf {
           policy random
       }
       reload
       ready {$POD_IP}:8081
   }

4. Click OK.
5. Choose ConfigMaps and Secrets in the navigation pane, select the kube-system namespace, and view the ConfigMap data of coredns to check whether the update is successful.

Configuring the Default Protocol Between the forward Plugin and the Upstream DNS Service

1. The NodeLocal DNSCache uses TCP to communicate with CoreDNS. CoreDNS communicates with the upstream DNS server based on the protocol used by the request source. By default, external domain name resolution requests from service containers pass through NodeLocal DNSCache and CoreDNS in sequence, and finally request the DNS server in the VPC using TCP.
2. The DNS server in the VPC supports TCP only to a limited extent. To use NodeLocal DNSCache, modify the CoreDNS configuration so that UDP is more appropriate to communicate with the upstream DNS server, preventing resolution exceptions. You are advised to use the following method to modify the CoreDNS configuration file:

   The forward plug-in is used to set the upstream nameservers. The following parameters are included:

   prefer_udp: Even if a request is received through TCP, UDP should be used first.

   If you want CoreDNS to preferentially use UDP to communicate with upstream systems, set the protocol in the forward plugin to prefer_udp. For details about the forward plugin, see https://coredns.io/plugins/forward/.

   1. Log in to the CCE console and click the cluster name to access the cluster console.
   2. In the navigation pane, choose Add-ons. Then, click Edit under CoreDNS.
   3. Edit extended parameters in Parameters and modify the following content in the plugins field:

      {
          "configBlock": "prefer_udp",
          "name": "forward",
          "parameters": ". /etc/resolv.conf"
      }

      Corefile:

      Corefile: |-
        .:5353 {
            bind {$POD_IP}
            cache 30 {
                servfail 5s
            }
            errors
            health {$POD_IP}:8080
            kubernetes cluster.local in-addr.arpa ip6.arpa {
                pods insecure
                fallthrough in-addr.arpa ip6.arpa
            }
            loadbalance round_robin
            prometheus {$POD_IP}:9153
            forward . /etc/resolv.conf {
                prefer_udp
            }
            reload
            ready {$POD_IP}:8081
        }

Properly Configuring a Cache Policy

If you configure CoreDNS with an upstream DNS server, you can implement a cache policy that enables CoreDNS to use the expired local cache when it is unable to access the upstream DNS server.

1. Log in to the CCE console and click the cluster name to access the cluster console.
2. In the navigation pane, choose Add-ons. Then, click Edit under CoreDNS.
3. Edit extended parameters in the Parameters area and modify the cache content in the plugins field. For details about how to configure the cache, see https://coredns.io/plugins/cache/.

   {
       "configBlock": "servfail 5s\nserve_stale 60s immediate",
       "name": "cache",
       "parameters": 30
   }

   

4. Click OK.
5. In the navigation pane, choose ConfigMaps and Secrets. Select the kube-system namespace, view the ConfigMap data of CoreDNS to check whether the update is successful.

   Corefile:

   .:5353 {
       bind {$POD_IP}
       cache 30 {
           servfail 5s
           serve_stale 60s immediate
       }
       errors
       health {$POD_IP}:8080
       kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           fallthrough in-addr.arpa ip6.arpa
       }
       loadbalance round_robin
       prometheus {$POD_IP}:9153
       forward . /etc/resolv.conf {
           policy random
       }
       reload
       ready {$POD_IP}:8081
   }