Question 81897 in Docker Question posted in
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How to pass dynamic build args via Compose file – Docker

I am currently building a container in my compose with a command

docker compose build --build-arg VAR_NAME=$(some_command) service_name

and I would like to build the same container with the simpler command docker compose build service_name, but I have not found a way to have docker compute the new output of some_command at each build.

To accomplish this I can freely change both the compose file and the Dockerfile for the container.

Is there any way to have docker instantiate a build argument or some other kind of variables dynamically on each build?

What I tried so far:

My first idea was to do something like the following

services:
    service_name:
        build:
            context: ./service_name
            args:
                VAR_NAME: $(some_command)

or

                VAR_NAME: "$(some_command)"

or

                VAR_NAME: "$$(some_command)"

but none of them works, even if

services:
    service_name:
        build:
            context: ./service_name
            args:
                VAR_NAME: 'example of some_command output'

works correctly.

Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    @tom's answer is likely better but out of stubbornness I decided to generate a docker-compose.ovverride.yml with the correct values.

    I went for ad-hoc template processed with sed:

    docker-compose.template:

    services:
    admin:
        build:
            args:
                VAR_NAME: __VAR_NAME__
                VAR_NAME2: __VAR_NAME2__

    and a simple sed script:

    sed 
  -e "s/__VAR_NAME__/$(some_command)/g" 
  -e "s/__VAR_NAME2__/$(some_command2)/g" 
  ./docker-compose.template 
  > ./docker-compose.override.yml

    This is quite ugly but works for my use-case

    TODO:

    1. Fix escaping in sed's regex pattern, currently the output is in the pattern [0-9]+ so it is fine
    2. Use a better template language

  2. 0

    it seems that docker does not support running shell commands in a docker-compose.yml

    see the Using shell command in docker-compose.yml github discussion

    you could use a script to wrap your build command.

    # build.sh

docker-compose build --build-arg MY_VAR=$(command)
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