Kubernetes: How to allow two pods running in same/different namespace communicate irrespective of the protocol using a servicename?

kubernetes kubernetes-service kubernetes-networkpolicy
Harsha G V picture Harsha G V · Sep 19, 2019 · Viewed 7.3k times · Source

Allow two pods (say pod A and B) running in same/different namespace communicate irrespective of the protocol(say http,https,akka.tcp) along with a valid Network policy applied.

Solutions tried:

  1. Tried applying network policy to both the pods and also used the service name: “my-svc.my-namespace.svc.cluster.local” to make pod B communicate to pod A which is running the service “my-svc” but both failed to communicate.

  2. Also tried adding the IP address and host mapping of pod A in pod B while it’s deployment, then pod B was able to communicate to pod A but inverse communication is failing.

Kindly suggest me a way to fix this.

Answer

weibeld picture weibeld · Sep 19, 2019

By default, pods can communicate with each other by their IP address, regardless of the namespace they're in.

You can see the IP address of each pod with:

kubectl get pods -o wide --all-namespaces

However, the normal way to communicate within a cluster is through Service resources.

A Service also has an IP address and additionally a DNS name. A Service is backed by a set of pods. The Service forwards requests to itself to one of the backing pods.

The fully qualified DNS name of a Service is:

<service-name>.<service-namespace>.svc.cluster.local

This can be resolved to the IP address of the Service from anywhere in the cluster (regardless of namespace).

For example, if you have:

  • Namespace ns-a: Service svc-a → set of pods A
  • Namespace ns-b: Service svc-b → set of pods B

Then a pod of set A can reach a pod of set B by making a request to:

svc-b.ns-b.svc.cluster.local

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