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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.

Harsha G V
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3 Answers3

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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
weibeld
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  • yes as mentioned in my 1st attempted solution, used similar service name [ _svc-a.ns-a.svc.cluster.local_ ] to communicate from Pod B to Pod A, but it failed. – Harsha G V Sep 20 '19 at 11:45
  • Did you add any NetworkPolicies or do any other settings? It should work by default in a fresh cluster. – weibeld Sep 20 '19 at 11:51
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You can put the Pods behind Services and use Service DNS for communication. Calls to service-name allow Pods in the same namespace to communicate. Calls to service-name.namespace allow Pods in different namespaces to communicate.

Alassane Ndiaye
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When trying to reach a service using it’s short name, a pod will look it up only in it’s own namespace, not across all namespaces in the cluster. So to answer your question: each Pod A will only talk to it’s “local” Pod B.

For a Pod A in one namespace to reach a Pod B in another namespace, you will need to use the fqdn of the service in ns2 which would be something like: ..svc.cluster.local.

Hassan Juma
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