Rails 4.2 with Docker not accessible

In the case you're a Rails developer working with Docker, migrating your application to Rails 4.2 introduced the issue that when starting the application, you cannot access it anymore.

Having a closer look to the logs shows us why:

=> Booting Puma
=> Rails 4.2.0 application starting in development on http://localhost:3000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Puma 2.11.0 starting...
* Min threads: 0, max threads: 16
* Environment: development
* Listening on tcp://localhost:3000

As you can see the Rails application is listening to localhost instead of 0.0.0.0.

The Rack default option of the binding parameter has been updated as described in this Github issue.

Fixing the issue with Fig

With Fig, updating the fig.yml file solves the issue:

web:
  build: .
  command: bundle exec bin/rails server -b 0.0.0.0
  ...

Adding the -b 0.0.0.0 fixes the issue.