The problem

I needed to fire up the Rails 3 server to listen on a port other than the default port 3000. Obviously, I could simply run it like this:

rails server -p 1234

However, for simplicity (and so I wouldn’t forget), I wanted to be able to configure the alternate port. It seems that the easiest way to accomplish that goal is by metaprogramming Rails::Server in config/boot.rb, as described in this StackOverflow answer.

However, I didn’t want to hack the port for everyone; I wanted a solution that would be specific to a RAILS_ENV setting.

A simple solution

The simplest solution (to me) was to provide for a config/config-local.yml file, keyed to each environment. For instance, to allow me to use port 1234 when RAILS_ENV is set to bmc, I’d simply put the following in that file:

# Local configuration.
#
# NOTE: This file is NOT supplied by Rails. See the logic at the bottom
# of boot.rb.
#
# port - TCP port on which to run the Rails server. Default: 3000
# -----------------------------------------------------------------------

bmc:
  port: 1234

It’s a simple matter to provide the necessary logic in config/boot.rb:

Note that the code is more general-purpose than merely what’s necessary to handle a TCP port override.

• The OPTIONS hash defines the default values for various configuration parameters.
• The fix_config_hash function recursively walks through a hash table, converting its string keys to Ruby symbols. It’s used to convert the parsed YAML file into a hash that can be merged with OPTIONS.
• The final merged configuration is stored in a LocalConfig global constant, which is accessible elsewhere in the Rails application.
• The configuration YAML file is preparsed with ERB, allowing ERB template logic in the YAML configurations.

Sample runs

When I use the development environment, Rails listens on the standard port:

$ RAILS_ENV=development rails server
Loading local configuration file /home/bmc/src/rails-test/config/config-local.yml
=> Booting Mongrel
=> Rails 3.1.0 application starting in development on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
^C
$

When I use the bmc environment, Rails listens on port 1234:

$ RAILS_ENV=bmc rails s
Loading local configuration file /home/bmc/src/rails-test/config/config-local.yml
=> Booting Mongrel
=> Rails 3.1.0 application starting in development on http://0.0.0.0:1234
=> Call with -d to detach
=> Ctrl-C to shutdown server
^C
$