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Configure custom CoreDNS

Supported Configurations
Running the control plane as a container with:

Customizing CoreDNS enables tailored DNS management for specific requirements, such as handling custom zones, forwarding DNS queries, and integrating with external DNS providers. This guide explains how to configure and use custom CoreDNS setups in a vCluster.

Common CoreDNS customizations​

The following are typical customizations for CoreDNS in vCluster:

  • Custom DNS zones: Define specific domains that resolve to selected IP addresses.
  • DNS forwarding: Route specific domain queries to external DNS servers.
  • Integration with external DNS providers: Connect to cloud provider DNS services.
  • Local DNS overrides: Define host entries for development or testing environments.

For more advanced configurations, see to the CoreDNS documentation.

Define CoreDNS configuration​

Create or modify the vcluster.yaml file to include a custom CoreDNS configuration using the overwriteManifests field:

controlPlane:
  backingStore:
    etcd:
      deploy:
        enabled: true
  coredns:
    overwriteManifests: |-
      apiVersion: v1
      kind: ConfigMap
      metadata:
        name: coredns
        namespace: kube-system
      data:
        Corefile: |-
          .:1053 {
            errors
            health
            ready
            rewrite name regex .*\.nodes\.vcluster\.com kubernetes.default.svc.cluster.local
            kubernetes cluster.local in-addr.arpa ip6.arpa {
              pods insecure
              fallthrough in-addr.arpa ip6.arpa
            }
            hosts /etc/NodeHosts {
              ttl 60
              reload 15s
              fallthrough
            }
            prometheus :9153
            forward . /etc/resolv.conf
            file /etc/coredns/dg.db dg.in
            cache 30
            loop
            loadbalance
          }
          import /etc/coredns/custom/*.server
        NodeHosts: ""
        dg.db: |
          dg.in. IN SOA ns3.dg.in cto.dg.in 20132601 10800 900 1209600 86400
          ; dg.in file
          *.dg.in. IN A 10.211.9.11
          *.dg.in. IN A 10.211.9.12
          *.dg.in. IN A 10.211.9.13
          *.dg.in. IN A 10.211.9.14
          *.dg.in. IN A 10.211.9.15
          *.dg.in. IN A 10.211.9.16

Apply your CoreDNS configuration​

After defining your CoreDNS configuration, choose one of these approaches based on your situation:

Deploy a new vCluster​

If you're creating a new vCluster, deploy it with your custom CoreDNS configuration using Helm:

helm install corednsissue loft/vcluster --version 0.20.0 -f vcluster.yaml

Update an existing vCluster​

If you already have a running vCluster:

  1. Update your vcluster.yaml with the new CoreDNS configuration or add additional entries:
da.db: |
  dada.in. IN SOA ns3.dada.in cto.da.in 20132601 10800 900 1209600 86400
  ; da.in file
  *.da.in. IN A 10.311.9.11
  *.da.in. IN A 10.311.9.12
  *.da.in. IN A 10.311.9.13
  *.da.in. IN A 10.311.9.14
  *.da.in. IN A 10.311.9.15
  *.da.in. IN A 10.311.9.16
  1. Apply the changes using Helm:
helm upgrade corednsissue loft/vcluster --version 0.20.0 -f vcluster.yaml

Test the DNS resolution​

After configuring custom CoreDNS settings, verify that the setup works correctly:

Verify ConfigMap changes​

Ensure the CoreDNS ConfigMap reflects your custom configuration:

kubectl get cm coredns -n kube-system -o yaml

Confirm CoreDNS pod status​

Check that CoreDNS pods are running and using the updated configuration:

kubectl get pods -n kube-system -l k8s-app=kube-dns

Test DNS resolution​

Use a test pod to validate that DNS resolution works for your custom zones:

kubectl run dns-test --image=busybox --restart=Never --rm -it -- nslookup myapp.da.in