Using Build Tools From Containers

You have to use a build tool that you do not want on your machine — what to do? Run it from a container, of course!

Fact: I do not like the JavaScript ecosystem, so I do not want to install npm and the like only because someone forces me to use it. For other tools or use cases, there may be more objective concerns. The question remains the same: How do I use a tool I can or will not install?

Here is an idea:

Start a container with the tool and its dependencies; most modern tools have images for CI pipelines.
Bind-mount the project directory into it.
Run the commands as you would usually do, but in the container.

This is, of course, not a novel idea; one half of GitHub Actions rests on this approach, after all. Wrapping it up so that it is easy to adopt and use holds some interest for me, though.

Specifically, for the example for Node.js, I created a Bash script $ along the lines of this:

if ! container_exists "${container_name}"; then
    docker run \
        --detach --rm \
        --name "${container_name}" \
        -v "$PWD":/usr/src/app \
        -w /usr/src/app \
        node:12-slim \
        tail -f /dev/null # block
fi

docker exec -it \
    -w /usr/src/app \
    "${container_name}" \
    "${@}"

I left out some fluff parts, and I also added some setup code to the container creation part for convenience.

Full source: Gist

So the first call would start the container — which is quick once you have the image — taking care to keep it alive. Then we just forward all parameters, including the actual command we want to run, to the containers.

I used it like so (in an existing project):

./$ npm install
./$ ncc index.js

All project files will be generated outside of the container; you will have to .gitignore and clean up just like you usually would. Do not forget docker kill $container_name either!

Future work:

Have the container automatically shut down after some idle time.
Generalize the script to make it a proper tool. (I solved a similar problem once before.)
Use a container runner that does not create files with root:root ownership.

I have since released container-do which is more general and robust than this script here.