A custom Dockerfile for a runner image

My Phoenix 1.6 app uses google-chrome-stable + chromedriver + wallaby during runtime to parse webpages and I’m currently stuck at adding chromedriver binary to a runner image.

Adding the necessary steps to the Dockerfile that’s automatically generated by flyctl at the root of the Phoenix project affects only the build image.

It looks like pushing an image with chromedriver and setting the ARG RUNNER_IMAGE="bla-bla" will help but it seems to be too much of a hassle.

Maybe there is an easier way?