Shackles allows multiple database environments and environment overrides to ActiveRecord, allowing least-privilege best practices.
gem 'shackles' to your Gemfile (tested with Rails 4.x and 5.x, and also
with the release candidate for Rails 6.0)
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'] .(ENV['RAILS_DATABASE_ENVIRONMENT'].to_sym) end if ENV['RAILS_DATABASE_USER'] .(: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