Adding a Dockerfile RUN command equivalent to docker-compose file

Question

Is there a way to add a Dockerfile RUN command equivalent to a compose file?

Context:

docker-compose.yaml has service webapp with an accompanying Dockerfile (webapp.Dockerfile)

When I do development, I have a docker-compose.local.yaml that adds some additional development configurations to webbapp service, e.g.:

services:
  webapp:
    stdin_open: true
    tty: true
    ... # other stuff for my local development needs

I'd also like to run a couple of commands to the image being built, but I do not want to put it in a RUN command in webapp.Dockerfile. I'd like to somehow include it in docker-compose.local.yaml so that it's something additional I can tack on without changing the base configs. (BTW I invoke the additional YAML file with COMPOSE_FILE environment variable).

Answer 1

A RUN command is part of the image build process; it can only be used in a Dockerfile. If I want to install additional commands into the image used by my compose configuration, I can build a new image based on the old one.

For example, if I have a docker-compose.yaml that looks like this:

services:
  web:
    image: docker.io/alpinelinux/darkhttpd:latest

And I really want the curl command to be available inside this container, I can create a docker-compose.override.yaml like this:

services:
  web:
    build: .

And then put a Dockerfile in the same directory as the docker-compose.yaml that looks like this:

services:
  web:
    image: development
    build:
      context: .

And when docker-compose up the environment, it will build the custom image and use that rather than using the image specified in docker-compose.yaml:

$ docker-compose up
Building web
[+] Building 0.1s (6/6) FINISHED
 => [internal] load build definition from Dockerfile                                                                                                     0.1s
 => => transferring dockerfile: 124B                                                                                                                     0.0s
 => [internal] load .dockerignore                                                                                                                        0.1s
 => => transferring context: 2B                                                                                                                          0.0s
 => [internal] load metadata for docker.io/alpinelinux/darkhttpd:latest                                                                                  0.0s
 => [1/2] FROM docker.io/alpinelinux/darkhttpd:latest                                                                                                    0.0s
 => CACHED [2/2] RUN apk add curl                                                                                                                        0.0s
 => exporting to image                                                                                                                                   0.0s
 => => exporting layers                                                                                                                                  0.0s
 => => writing image sha256:23e53345322fa1787aa6fd291347732501499f60656805675c6fd4217d040006                                                             0.0s
 => => naming to docker.io/library/development                                                                                                           0.0s
WARNING: Image for service web was built because it did not already exist. To rebuild this image you must use `docker-compose build` or `docker-compose up --build`.
Creating containers_web_1 ... done
Attaching to containers_web_1
web_1  | darkhttpd/1.14, copyright (c) 2003-2022 Emil Mikulic.