The command element in the compose file behaves strange

Docker Engine General
1

Hi,

I have a parent docker image and multiple another images based on the parent image. I only set the ENTRYPOINT in the parent’s Dockerfile. There is no ENTRYPOINT declaration in the child images. Everything works fine, my child images run properly. When I start running a child image then the script that I set in the parent image is executed as I expected.

Now I would like to overwrite the ENTRYPOINT for one of my child image and run another “business logic” before I continue, so I added a command element into the docker compose file. According to the documentation this will overwrite the original entrypoint and run my new bash script that is of course, available in the container.

But what I see is the following:
The child image is still executing the original command, defined in the parent’s ENTRYPOINT and the command I added to the command element of the compose file became parameters of the entripoint bash script instead of execute it.

Dockerfile of the basic image:

# parent:0.0.1
FROM alpine:3.21.0
...
COPY container-scripts/entrypoint.sh container-scripts/do-something-else.sh /
ENTRYPOINT ["/entrypoint.sh"]
````

Child image:

# child:0.0.1
FROM parent:0.0.1
...
# no entrypoint declaration
````

compose file:

services:
    start-first:
        image:  child:0.0.1
        ...
        
    run-after:
        image:  child:0.0.1
        command: ["/do-something-else.sh"]
        ...

and then the do-something-else.sh:

#!/bin/bash -ue
echo "do something else..."
echo "$@"
exec /entrypoint.sh

But the /do-something-else.sh became the parameter of the original entripoint.sh instead of executing the script.

$ docker inspect parent
[
    {
        "Id": "6399bfc0f0d8ba39e8af41feb50131053dd734535537d47336ef297d21fdb34f",
        "Created": "2025-02-03T15:01:50.034149716Z",
        "Path": "/entrypoint.sh",
        "Args": [
            "wait-for-container.sh"
        ],
        ...

What I missed here?

2

The command property specifies the parameters to be entered after the entrypoint
The child image inherits the entrypoint from the parent image and does not write over it

If you want no entrypoint, simply specify it empty in the compose file

services:
  run-after:
    image: child:0.0.1
    entrypoint: ""
    command: ["/do-something-else.sh"]
    # OR
    entrypoint: ["/do-something-else.sh"]
    ...
3

It works like a charm, thanks a lot. You saved my day.