Chapter 4. DNS Operator in OpenShift Container Platform

1. Use the oc get command to view the Deployment status:

   $ oc get -n openshift-dns-operator deployment/dns-operator

   Example output

   NAME           READY     UP-TO-DATE   AVAILABLE   AGE
   dns-operator   1/1       1            1           23h

   ClusterOperator is the Custom Resource object which holds the current state of an operator. This object is used by operators to convey their state to the rest of the cluster.

2. Use the oc get command to view the state of the DNS Operator:

   $ oc get clusteroperator/dns

   Example output

   NAME      VERSION     AVAILABLE   PROGRESSING   DEGRADED   SINCE
   dns       4.1.0-0.11  True        False         False      92m

   AVAILABLE, PROGRESSING and DEGRADED provide information about the status of the operator. AVAILABLE is True when at least 1 pod from the CoreDNS DaemonSet is reporting an Available status condition.

Procedure

1. Use the oc describe command to view the default dns:

   $ oc describe dns.operator/default

   Example output

   Name:         default
   Namespace:
   Labels:       <none>
   Annotations:  <none>
   API Version:  operator.openshift.io/v1
   Kind:         DNS
   ...
   Status:
     Cluster Domain:  cluster.local 1
     Cluster IP:      172.30.0.10 2
   ...

   1

   The Cluster Domain field is the base DNS domain used to construct fully qualified Pod and Service domain names.

   2

   The Cluster IP is the address pods query for name resolution. The IP is defined as the 10th address in the Service CIDR range.

2. To find the Service CIDR of your cluster, use the oc get command:

   $ oc get networks.config/cluster -o jsonpath='{$.status.serviceNetwork}'

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.

   Note

   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 DaemonSet.