Debugging Rails Apps Running in docker-compose Using byebug

The Problem

You are serving a rails application from inside Docker Compose and want to use byebug to set breakpoints and debug your app, but your breakpoints are not stopping execution and you can’t interact with byebug.

Enable interaction with your container

First you need to configure your container (via docker-compose.yml) to enable interaction via stdin and tty:

container_name:
  ...
  stdin_open: true
  tty: true

For details see here.

Run docker-compose in detached mode

$ docker-compose up -d

View container logs

Usually docker-compose up will echo all of your containers’ logs to stdout, but this does not happen when running in detached mode. Use docker-compose logs to watch the log output:

$ docker-compose logs --follow --tail=0

Attach to your app to interact with byebug

Once your app is up and running in its container you can attach to it with docker attach:

$ docker attach <container_name>

Since you configured stdin and tty, you’ll be able to interact with byebug.

Stop your containers when finished

Once you’re done you can stop your containers with docker-compose stop.