This question on pod-to-pod communication basically says that Services will help look-up the actual pod for communication.
Excerpt from answer
You need to create a Service to expose the Pod's port and then you just need to use the Service name and kube-dns will resolve the Pod's IP address
I am not clear as to what is the communication protocol between the pods. Is it HTTP(S)? Can I use AMQP? gRPC?
It is basic IP in the TCP/IP.
Therefore, if you install an AMQP in the pod, it will use the TCP/IP that kubernetes is providing to resolve host and IP etc to provide its AMQP.
If you set up a tomcat, it will use the underlying TCP/IP to provide its HTTP(s).
I hope it clarifies.