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/CoreDNS with ETCD backend on EKS/

CoreDNS with ETCD backend on EKS

0

CoreDNS has a ETCD plugin https://coredns.io/plugins/etcd/, which essentially allows for dynamic DNS by reading the values from ETCD.

Since EKS is managed, it means we can't access the etcd instance on master node, that's fine as I can create my own etcd cluster (and I did). Below is my coredns deployment

apiVersion: v1
data:
  Corefile: |
    .:53 {
        errors
        health
        log
        kubernetes cluster.local in-addr.arpa ip6.arpa {
          pods insecure
          fallthrough in-addr.arpa ip6.arpa
        }
        etcd {
            path /skydns
            endpoint http://etcd-cluster-ip.default.svc.cluster.local:2379
            fallthrough
        }
        prometheus :9153
        forward . /etc/resolv.conf
        cache 30
        loop
        reload
        loadbalance
    }
kind: ConfigMap
metadata:
  annotations: {}
  labels:
    eks.amazonaws.com/component: coredns
    k8s-app: kube-dns
  name: coredns
  namespace: kube-system

The issue I face now is that the master node is not able to resolve the ClusterIP DNS etcd-cluster-ip.default.svc.cluster.local, which is the ClusterIP of my etcd cluster. If I change that DNS with the actual ClusterIP, name resolution works as expected and CoreDNS is able to access ETCD

How can the master node resolve the DNS of my cluster ? I see below line in coredns logs

{"level":"warn","ts":"2022-03-16T20:44:42.352Z","caller":"clientv3/retry_interceptor.go:61","msg":"retrying of unary invoker failed","target":"endpoint://client-fd406ba0-cc21-4132-bfef-ca14e3fd4eb3/etcd-cluster-ip.default.svc.cluster.local:2379","attempt":0,"error":"rpc error: code = DeadlineExceeded desc = latest balancer error: all SubConns are in TransientFailure, latest connection error: connection error: desc = \"transport: Error while dialing dial tcp: lookup etcd-cluster-ip.default.svc.cluster.local on 10.0.0.2:53: no such host\""}
asked 2 months ago18 views
1 Answers
0

I believe you are encountering the same issue as described in this CoreDNS issue - https://github.com/coredns/coredns/issues/2159

As per this comment, your desired setup will work only if the FQDN of the ETCD server can be resolved outside the cluster.

The work-around is to directly specify the ClusterIP of your ETCD service in the Corefile endpoint configuration, and I see that you are already using this approach.

The bottom line is that your CoreDNS pod cannot use itself to perform DNS resolution.

I hope this helps!

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answered 2 months ago

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