4.3. Using DNS forwarding

Procedure

1. Modify the DNS Operator object named default:

   $ oc edit dns.operator/default

   This allows the Operator to create and update the ConfigMap named dns-default with additional server configuration blocks based on Server. If none of the servers has a zone that matches the query, then name resolution falls back to the name servers that are specified in /etc/resolv.conf.

   Sample DNS

   apiVersion: operator.openshift.io/v1
   kind: DNS
   metadata:
     name: default
   spec:
     servers:
     - name: foo-server 

   1

   
       zones: 

   2

   
         - foo.com
       forwardPlugin:
         upstreams: 

   3

   
           - 1.1.1.1
           - 2.2.2.2:5353
     - name: bar-server
       zones:
         - bar.com
         - example.com
       forwardPlugin:
         upstreams:
           - 3.3.3.3
           - 4.4.4.4:5454

   1

   name must comply with the rfc6335 service name syntax.

   2

   zones must conform to the definition of a subdomain in rfc1123. The cluster domain, cluster.local, is an invalid subdomain for zones.

   3

   A maximum of 15 upstreams is allowed per forwardPlugin.

   注意

   If servers is undefined or invalid, the ConfigMap only contains the default server.

2. View the ConfigMap:

   $ oc get configmap/dns-default -n openshift-dns -o yaml

   Sample DNS ConfigMap based on previous sample DNS

   apiVersion: v1
   data:
     Corefile: |
       foo.com:5353 {
           forward . 1.1.1.1 2.2.2.2:5353
       }
       bar.com:5353 example.com:5353 {
           forward . 3.3.3.3 4.4.4.4:5454 

   1

   
       }
       .:5353 {
           errors
           health
           kubernetes cluster.local in-addr.arpa ip6.arpa {
               pods insecure
               upstream
               fallthrough in-addr.arpa ip6.arpa
           }
           prometheus :9153
           forward . /etc/resolv.conf {
               policy sequential
           }
           cache 30
           reload
       }
   kind: ConfigMap
   metadata:
     labels:
       dns.operator.openshift.io/owning-dns: default
     name: dns-default
     namespace: openshift-dns

   1

   Changes to the forwardPlugin triggers a rolling update of the CoreDNS daemon set.