Pass a variable to a Dockerfile from a docker-compose.yml file

Question

I have several docker-compose.yml files that I want to use the same Dockerfile with, with a slight variation. So I want to pass an argument to that Dockerfile so that I can do something slightly different depending on whatever value the variable is set to.

What I have tried so far

docker-compose-A.yml file

version: '2'  services:   django:     build:       context: .       dockerfile: ./docker/Dockerfile       args:         - SOMETHING=foo 

docker-compose-B.yml file

version: '2'  services:   django:     build:       context: .       dockerfile: ./docker/Dockerfile       args:         - SOMETHING=bar 

I have a dockerfile I want to use SOMETHING in. e.g.

# Dockerfile RUN echo $SOMETHING 

That doesn't work. SOMETHING is not passed to the dockerfile.

Am I doing this incorrectly or is this not the intended usage?

Is there any other way to pass a variable to a Dockerfile from a docker-compose.yml file?

Answer 1

Basically I missed declaring the arg in the Dockerfile.

# docker-compose.yml file  version: '2'  services:   django:     build:       context: .       dockerfile: ./docker/Dockerfile       args:         - SOMETHING=foo 

 

# Dockerfile ARG SOMETHING RUN echo $SOMETHING 

Shoutout to @Lauri for showing me the light.