Docker for Rails Developers

Debugging

No chapter on testing would be complete without some mention of how to debug our application when it isn’t behaving as we’d expect.

Imagine there’s a problem with our welcome_controller.rb. Let’s use the byebug debugger that’s included as standard with a Rails app. Let’s add a byebug breakpoint to our welcome_controller.rb:

class WelcomeController < ApplicationController
  def index
    redis = Redis.new(host: "redis", port: 6379)
    redis.incr "page hits"

    @page_hits = redis.get "page hits"
    byebug
  end
end

Let’s stop our Rails server:

$ docker-compose stop web

When we want an interactive session with a container, rather than using docker-compose up, we instead use docker-compose run. Let’s ...