Locking your Rails app to specific gem versions

To lock in a gem, you can modify your environments files, like how

config/environments.rb

has

# Require Rails gems.
require 'rubygems'
require_gem 'activerecord'
require_gem 'actionpack'
require_gem 'actionmailer'
require_gem 'rails'

Change it to the versions you are using, like

# Require Rails gems.
require 'rubygems'
require_gem 'activerecord', '<= 1.30'
require_gem 'actionpack', '<= 1.1.0'
require_gem 'actionmailer', '<= 0.5.0'
require_gem 'rails', '<= 0.9.1'