Registry doesn't work with random host port binding

[britter]

For testing it's often desirable to start off a throwaway container and then create a port binding to a random host port. It looks however like the registry does not work if no explicit host port is passed to the run command:

$ docker run -d -p 5000 registry:2.8.1
068657e6b2f9ef4c3f7927b966bd4c0579aea6274832f34cfc6390bd901e8b76

$ docker ps
CONTAINER ID   IMAGE            COMMAND                  CREATED         STATUS         PORTS                     NAMES
068657e6b2f9   registry:2.8.1   "/entrypoint.sh /etc…"   3 seconds ago   Up 2 seconds   0.0.0.0:56997->5000/tcp   gallant_fermi

$ docker pull busybox:1.33.0
1.33.0: Pulling from library/busybox
Digest: sha256:315fd9e7f9056a6d76dfc2c63a5377c37aaa79faed354dce683147ed781adc77
Status: Image is up to date for busybox:1.33.0
docker.io/library/busybox:1.33.0

$ docker tag busybox:1.33.0 localhost:56997/busybox:1.33.0

$ docker push localhost:56997/busybox:1.33.0
The push refers to repository [localhost:56997/busybox]
Get "http://localhost:56997/v2/": dial tcp [::1]:56997: connect: connection refused

The same works if the port binding in the run command is set up using an explicit host port like -p 5000:5000.

[a-naitslimane]

My scenario is a bit different, i.e: I would like to run more than one instance of the image in order to have multiple containers (registries) running each on a different port. I guess we need to build a custom image for that?

[milosgajdos]

My scenario is a bit different, i.e: I would like to run more than one instance of the image in order to have multiple containers (registries) running each on a different port. I guess we need to build a custom image for that?

Why don't you just portmap to the ports you need? Run 3 different instances with registry container port being portmapped to different ports on the host

[davinkevin]

@milosgajdos I suspect the registry returns the port used in some request, like redirection or absolute links (part of the container protocol maybe).

[a-naitslimane]

My scenario is a bit different, i.e: I would like to run more than one instance of the image in order to have multiple containers (registries) running each on a different port. I guess we need to build a custom image for that?

Why don't you just portmap to the ports you need? Run 3 different instances with registry container port being portmapped to different ports on the host

Because there is a "LISTEN $SPECIFIC_PORT" somewhere in the definition of the Dockerfile of the original image. And that specific $SPECIFIC_PORT value is 5000.

In fact I have finally found the answer in the documentation here: https://distribution.github.io/distribution/about/deploying/#customize-the-published-port

Basically, there's an environment variable which could be set for the container's destination port: REGISTRY_HTTP_ADDR

The example they gave was to listen on port 5001 from any IP, like so: REGISTRY_HTTP_ADDR=0.0.0.0:5001

By the way, my real problem using Docker Desktop for windows turned out to be that I was trying to hard map the 5000 container's port, with the host to 6000, so in my docker-compose.yaml file:

ports:
      - 127.0.0.1:6000:5000

I made a few searches and found out that the 6000 port was bocked by default on many systems/browsers. So avoid mapping the 6000 for the host