CoreDNS Lameduck

Adding lameduck to the health plugin minimizes DNS resolution failures during a CoreDNS pod restart or deployment rollout. Mirantis Kubernetes Engine (MKE) supports enabling lameduck for the default server block.

Configuration

CoreDNS lameduck support is disabled by default. To enable lameduck, configure the lameduck section of the MKE configuration file under dns:

  dns:
    lameduck:
      enabled: true
      duration: "7s"

Configuration parameters

MKE 4 does not support the use of the kubectl edit command to edit the CoreDNS config map outside of MKE for the purpose of configuring the lameduck function. Any such changes will be overwritten by the values set in the MKE configuration file whenever you execute the mkectl apply command.

Applying configuration

1. Enable or adjust the lameduck configuration.

2. Wait for the CoreDNS pods to apply the changes.

3. Check the CoreDNS logs to verify that the Pod is running and that it has applied the configuration without any errors.

   kubectl logs -f deployment/coredns -n kube-system

   Example output:

   Found 2 pods, using pod/coredns-5d78c9869d-7qfnd
   .:53
   [INFO] plugin/reload: Running configuration SHA512 = 591cf328cccc12bc490481273e738df59329c62c0b729d94e8b61db9961c2fa5f046dd37f1cf888b953814040d180f52594972691cd6ff41be96639138a43908
   CoreDNS-1.10.1
   go1.20, 055b2c3
   
   [INFO] Reloading
   [INFO] plugin/reload: Running configuration SHA512 = 26fe33ee13757f04c8c9a1caebd7c6f0614306c92089ea215f1a8663f95ff1e673d4fa5de544b31492231923d4679370ce8735823ce3b5e65e5c23a9029c4512
   [INFO] Reloading complete

4. View the ConfigMap to verify the configuration that was applied:

   kubectl describe configmap coredns -n kube-system

   Example output:

   Name:         coredns
   Namespace:    kube-system
   Labels:       k0s.k0sproject.io/stack=coredns
   Annotations:  k0s.k0sproject.io/last-applied-configuration:
                   {"apiVersion":"v1","data":{"Corefile":".:53 {\n    errors\n    health\n    ready\n    kubernetes cluster.local in-addr.arpa ip6.arpa {\n  ...
                 k0s.k0sproject.io/stack-checksum: df0a18b174e12f166824f894f447d08f
   
   Data
   ====
   Corefile:
   ----
   .:53 {
     cache 30
     errors
     forward . /etc/resolv.conf
     health {
       lameduck 7s
     }
     kubernetes cluster.local in-addr.arpa ip6.arpa {
       pods insecure
       ttl 30
       fallthrough in-addr.arpa ip6.arpa
     }
     loadbalance
     loop
     prometheus :9153
     ready
     reload
   }
   
   
   BinaryData
   ====
   
   Events:  <none>

Lameduck configuration parameters