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Shackles

About

Shackles allows multiple database environments and environment overrides to ActiveRecord, allowing least-privilege best practices.

Installation

Add gem 'shackles' to your Gemfile (tested with Rails 2.3 and 3.2)

Usage

There are two major use cases for shackles. The first is for master/slave(/deploy) environments. Using a slave is as simple as adding a slave block (underneath your main environment block) in database.yml, then wrapping stuff you want to query the slave in Shackles.activate(:slave) blocks. You can extend this to a deploy environment so that migrations will run as a deploy user that permission to modify schema, while your normal app runs with lower privileges that cannot modify schema. This is defense-in-depth in practice, so that if you happen to have a SQL injection bug, it would be impossible to do something like dropping tables.

The other major use case is more defense-in-depth. By carefully setting up your environment, you can default to script/console sessions for regular users to use their own database user, and the slave.

Example database.yml file:

production:
  adapter: postgresql
  username: myapp
  database: myapp
  host: db-master
  slave:
    host: db-slave
  deploy:
    username: deploy

Using an initializer, you can achieve the default environment settings (in tandem with profile changes):

if ENV['RAILS_DATABASE_ENVIRONMENT']
  Shackles.activate!(ENV['RAILS_DATABASE_ENVIRONMENT'].to_sym)
end
if ENV['RAILS_DATABASE_USER']
  Shackles.apply_config!(:username => ENV['RAILS_DATABASE_USER'])
end

Additionally in Ruby 2.0+ you can include Shackles::HelperMethods and use several helpers to execute methods on specific environments:

class SomeModel
  include Shackles::HelperMethods

  def expensive_read_only
    ...
  end
  shackle_method :expensive_read_only, environment: :slave

  def self.class_level_expensive_read_only
    ...
  end
  shackle_class_method :class_level_expensive_read_only, environment: :slave

  # helpers for multiple methods are also available

  shackle_methods :instance_method_foo, :instance_method_bar, environment: :slave
  shackle_class_methods :class_method_foo, :class_method_bar, environment: :slave
end