docker-compose evaluate expression in command array

I have below docker-compose.yml file. In the command section I would like to evaluate the curl expression before the command is passed to docker engine i.e. my curl should be evaluated first and then my container should run with -ip 10.0.0.2 option.

version: '2'
services:
  registrator:
    image: gliderlabs/registrator:v7
    container_name: registrator
    volumes:
      - /var/run/docker.sock:/tmp/docker.sock
    command: ['-ip', '$$(curl -X GET -s http://169.254.169.254/latest/meta-data/local-ipv4)']

This however is not being evaluated and my option is passed as -ip $(curl -X GET -s http://169.254.169.254/latest/meta-data/local-ipv4)

The respective docker run command however correctly evaluates the expression and my container is correctly starting with -ip 10.0.0.2 option:

docker run -v /var/run/docker.sock:/tmp/docker.sock gliderlabs/registrator:v7 -ip $(curl -X GET -s http://169.254.169.254/latest/meta-data/local-ipv4)

Solution

The docker command on the command line will work as the command will be executed by the shell and not the docker image, so it will be resolved.

the docker-compose command will override the default command (CMD) (see https://docs.docker.com/compose/compose-file/#command) so it will not be executed before the container is started but as the primary command in the container...

you could do something like:

version: '2'
services:
  registrator:
    image: gliderlabs/registrator:v7
    container_name: registrator
    volumes:
      - /var/run/docker.sock:/tmp/docker.sock
    command: ['-ip', '${IP}']

and run it with:

IP="$(curl -X GET -s http://169.254.169.254/latest/meta-data/local-ipv4)" docker-compose up

this will run it in the shell again and assign it to a variable called IP witch will be available during the docker-compose up command. You could put that command in a shell script to make it easier.