Chapter 5. 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

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 daemon set reports 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 upstream DNS servers.

   Sample DNS

   apiVersion: operator.openshift.io/v1
   kind: DNS
   metadata:
     name: default
   spec:
     servers:
     - name: foo-server 1
       zones: 2
       - example.com
       forwardPlugin:
         policy: Random 3
         upstreams: 4
         - 1.1.1.1
         - 2.2.2.2:5353
     - name: bar-server
       zones:
       - bar.com
       - example.com
       forwardPlugin:
         policy: Random
         upstreams:
         - 3.3.3.3
         - 4.4.4.4:5454
     upstreamResolvers: 5
       policy: Random 6
       upstreams: 7
       - type: SystemResolvConf 8
       - type: Network
         address: 1.2.3.4 9
         port: 53 10

   1

   Must comply with the rfc6335 service name syntax.

   2

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

   3

   Defines the policy to select upstream resolvers. Default value is Random. You can also use RoundRobin, and Sequential.

   4

   A maximum of 15 upstreams is allowed per forwardPlugin.

   5

   Optional. You can use it to override the default policy and forward DNS resolution to the specified DNS resolvers (upstream resolvers) for the default domain. If you do not provide any upstream resolvers, the DNS name queries go to the servers in /etc/resolv.conf.

   6

   Determines the order in which upstream servers are selected for querying. You can specify one of these values: Random, RoundRobin, or Sequential. The default value is Sequential.

   7

   Optional. You can use it to provide upstream resolvers.

   8

   You can specify two types of upstreams - SystemResolvConf and Network. SystemResolvConf configures the upstream to use `/etc/resolv.conf and Network defines a Networkresolver. You can specify one or both.

   9

   If the specified type is Network, you must provide an IP address. address must be a valid IPv4 or IPv6 address.

   10

   If the specified type is Network, you can optionally provide a port. port must be between 1 and 65535.

   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: |
       example.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 1.2.3.4:53 {
               policy Random
           }
           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.