Unable to reach localhost:8888 from host with docker-compose

Build Environment
1

I use docker-compose to run docker-compose run myname mycommand. That starts a Python web server on 0.0.0.0:8888. I can see the container running with: docker-compose ps. It’s here and it looks something like this (from an SSH session):

root@215a24ba17c2:~/buildhub2# docker-compose -f docker-compose.ci.yml ps
        Name                       Command               State           Ports
---------------------------------------------------------------------------------------
buildhub2_autograph_1   /bin/sh -c /go/bin/autograph     Up      8000/tcp
buildhub2_db_1          docker-entrypoint.sh postgres    Up      5432/tcp
buildhub2_memcached_1   docker-entrypoint.sh memcached   Up      11211/tcp
buildhub2_web_run_3     /bin/bash /app/bin/run.sh  ...   Up      0.0.0.0:8888->8888/tcp
elasticsearch           /bin/bash bin/es-docker          Up      9200/tcp, 9300/tcp

But I can’t curl localhost:8888 from the host. That’s what I want to do next to do some testing. From an SSH session:

root@215a24ba17c2:~/buildhub2# curl localhost:8888
curl: (7) Failed to connect to localhost port 8888: Connection refused

I tried 127.0.0.1:8888 and 0.0.0.0:8888 also.

My Dockerfile has EXPOSE 8888 in it and my docker-compose.yml has:

    ports:
      - "8888:8888"

…in the relevant container.

2

Usually the issue here is that you’ve not waited long enough for the container server to settle down. Try getting an SSH session after a failing build, and see if the container is still up. If it is, exec a shell on the container and see what processes are running inside it, to see if there is another issue.

3

No that wasn’t it.

I’ve probably solved it now since I posted my question. What I did instead, was using a second container in docker-compose that depends_on the Python web server. Now, from this other (new) container I can connect to the python web server on http://web:8888. The docker-compose looks something like this:

web:
  build:
    context: .
    dockerfile: Dockerfile
  image: kinto:build
  depends_on:
    - db
    - memcached
  ports:
    - "8888:8888"
  command: start

tests:
 build:
   context: .
   dockerfile: tests/Dockerfile
 image: kinto:tests
 depends_on:
   - web
 command: test

Now, inside that tests container I can successfully run curl web:8888.

I think there are some “quirks” about how networking works in Linux vs macOS. Or perhaps CircleCI vs. macOS. In my macOS host I was able to use curl localhost:8888.

This new solution feels more right but I wish I had more time to understanding docker networking in detail and to explain why the host can’t reach into a running container that exposes a port.

4

Yes, that makes sense - Docker Compose internally makes containers available using their services names as DNS names. However, that doesn’t explain why your port publishing does not work in your first-level (build) container. I wonder if you need nstat (with appropriate switches) to examine what ports are captured?

Hmm, also: since it is published to 0.0.0.0, try ifconfig in the build container to see what other interfaces are available. Perhaps it has bound to the LAN IP instead?