OpenShift: DNS Server Misbehaving

Zhimin Wen
4 min readJan 16
Image by Arek Socha from Pixabay

I am deploying an Operator based product onto the OpenShift cluster, however the reconciling error message of the operator gives me,

DNS Error: Server Misbehaving. Please check DNS Settings.

Sure enough, the DNS server is having problem. But it worth a study on how the DNS system works in the OpenShift cluster.

Resolving HTTP Handler

Lets have a toy HTTP handler program to resolve a hostname.

func dnscheck(w http.ResponseWriter, r *http.Request) {
host := r.FormValue("host")
resolver := net.Resolver{}
ips, err := resolver.LookupIPAddr(r.Context(), host)
if err != nil {
fmt.Fprintf(w, "Failed to resolve %s: %v", host, err)
} else {
fmt.Fprintf(w, "Resolved %s to %v", host, ips)

Build the container image, push into the OpenShift registry, deploy as a Deployment, expose the service. Then we can test it as below,

We can resolve a service name within in the same namespace. (Command breaks into two lines just for viewing purpose)

curl "\
Resolved app-service to [{ }]

We can also resolve a external name such as,

curl "\
Resolved to [{ } { } { } { } { } { } {2607:f8b0:4023:1000::71 } {2607:f8b0:4023:1000::8b } {2607:f8b0:4023:1000::65 } {2607:f8b0:4023:1000::64 }]

Name Resolving in a Pod

When a pod is being deployed, based on the .spec.dnsPolicy settings the kubelet will create the /etc/resolv.conf for the pods, where the DNS server for the pods is specified,

The default value for dnsPolicy is “ClusterFirst”, then what we will have for /etc/resolv.conf is listed as below,

oc exec -it app-6ccb45c4f7-whsxh -- bash -c "cat /etc/resolv.conf"

search dns-misbehaving.svc.cluster.local svc.cluster.local cluster.local
options ndots:5
Zhimin Wen