host.docker.internal vs container name when referencing ip

Question

When defining services in a docker-compose file, when do I use host.docker.internal for the host's ip and when do I need to use the container's name?

Answer 1

All possible communication flows are illustrated here:

(1): non-containerized process communicates with a container

(2): container communicates with another container

(3): the opposite direction of (1)

---

(1): container must forward port to host, so the non-containerized process can access it

services:
   c1:
    ...
     ports:
       - hostport:containerport

(2): container c1 just use the service name (container name - c2) to communicate with c2

(3): container c2 must Use host.docker.internal to communicate with host

Answer 2

If you want to connect from a container to a service on the host, use host.docker.internal . Be aware, that this special DNS name is only available on Windows and macOS.

Use the container name for networking between containers.