How to debug a rails app in docker with pry?

Question

I have a rails app running in a docker container in development environment.

When I try to debug it with placing binding.pry somewhere in the code and attaching to the container I can see the pry prompt in the output but it doesn't pause on it and I can't interact with it like it was without docker container.

So how do I debug a containerized app?

Answer 1

If you're using docker-compose, you can add these flags to docker-compose.yml:

app:   tty: true   stdin_open: true 

And then attach to your process with docker attach project_app_1. pry-rails works here now. Ensure less is installed on your container for the optimal pry experience.

cf. https://github.com/docker/compose/issues/423#issuecomment-141995398

Answer 2

to use pry you have to run it differently:

docker-compose run --service-ports web

check out this article for more info:

http://blog.carbonfive.com/2015/03/17/docker-rails-docker-compose-together-in-your-development-workflow/