docker-compose 'command' keyword gives: "FATAL: Command <COMMAND> not found."

Question

When executing docker-compose up --build I get the error FATAL: Command <COMMAND> not found. My docker-compose.yaml file.

version: '3'

services:
    gitlab-runner:
        container_name: gitlab-runner
        image: gitlab/gitlab-runner:v15.8.2
        volumes:
            - ./config:/etc/gitlab-runner
            - ./sock:/var/run/docker.sock
        command: bash -c "echo '123.123.255.11 adc.cde.com' >> /etc/hosts"

The command i put there does not really matter. I get the same error for every command I've tried so far (ls, cd, /bin/bash, sh, /bin/sh, or a shell script I copied to a volume). How do I get this to execute?

As a side node: Is there another way i could automatically modify a file on container-startup?

Docker Compose version 2.22.0 used image: gitlab/gitlab-runner:v15.8.2

I know for a fact, that bash is available on this image, since docker exec -it <container> bash does work (as well as all the other things I listed).

Answer 1

The image gitlab/gitlab-runner:v15.8.2 defines an ENTRYPOINT script:

$ docker image inspect gitlab/gitlab-runner:v15.8.2
...
            "Entrypoint": [
                "/usr/bin/dumb-init",
                "/entrypoint"
            ],
...

The entrypoint script ultimately runs:

exec gitlab-runner "$@"

So when you set:

command: /usr/bin/bash -c "echo '123.123.255.11 adc.cde.com' >> /etc/hosts"

You are actually running:

gitlab-runner /usr/bin/bash -c "echo ..."

And /usr/bin/bash isn't a valid gitlab-runner command, hence the error.

---

Ignoring all of the above, there's a more fundamental problem with your current configuration. If it worked as you intended and ran the bash command line, the container would simply exit immediately (because a container exists when the initial command exits).

For what you're trying to do, the simplest solution is to use the extra_hosts option in your compose file:

services:
  gitlab-runner:
    container_name: gitlab-runner
    image: gitlab/gitlab-runner:v15.8.2
    volumes:
      - ./config:/etc/gitlab-runner
      - ./sock:/var/run/docker.sock
    extra_hosts:
      - adc.cde.com:123.123.255.11

Once the container is running, we see:

$ docker exec gitlab-runner cat /etc/hosts
127.0.0.1       localhost
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
123.123.255.11  adc.cde.com
172.27.0.2      61da9a89d42f