switches

Switches lets you turn on and off sections of your code with Switches.foobar? booleans.

It's an extraction from http://brighterplanet.com, where we use it as an emergency button to turn on/off API integration with Facebook, Campaign Monitor, etc.

Quick start

Add 2 lines to config/environment.rb:

require File.join(File.dirname(__FILE__), 'boot')
[...]
require 'switches'                                  # AFTER boot, BEFORE initializer
[...]
Rails::Initializer.run do |config|
[...]
  config.gem 'switches', :lib => false              # INSIDE initializer

Now run this:

my-macbook:~/my_app $ ./script/runner 'Switches.setup'

Add your defaults to config/switches/defaults.yml:

--- 
ssl: true                   # ssl support is on by default
campaign_monitor: true      # campaign monitor integration is on by default

Tasks

Rake task	Cap task	Notes
rake s:c	cap TARGET s:c	show current switches
rake s:d	cap TARGET s:d	show difference between current and default switches
rake s:on[SWITCH]	cap TARGET s:on ARG=SWITCH	turn on SWITCH
rake s:off[SWITCH]	cap TARGET s:off ARG=SWITCH	turn off SWITCH
rake s:clear[SWITCH]	cap TARGET s:clear ARG=SWITCH	clear any switch for SWITCH
rake s:reset	cap TARGET s:reset	go back to defaults (deletes `config/switches/current.yml`)
rake s:backup	cap TARGET s:backup	backup current switches (copies to `config/switches/backup.yml`)
rake s:restore	cap TARGET s:restore	restore backed-up switches (copies `backup.yml` to `current.yml`)
rake s:default	cap TARGET s:default	list default settings

Throwing switches remotely with Capistrano

This is the minimum needed in the TARGET task:

task :production do
  role :app, 'ec2-88-77-66-55.compute-1.amazonaws.com'
  role :app, '177.133.33.144'

  set :rails_env, 'production'
  set :deploy_to, '/data/my_app'
  set :gfs, false
end

The switches will get applied to any role that matches /app/ (so :app_master, :app, etc.)

Throwing switches before you db:migrate

I like to use Switches to turn off %w{memoization caching facebook campaign_monitor delayed_job} before running rake db:migrate, so I put this in lib/tasks/databases.rake:

namespace :db do
  # what to do before db:migrate
  task :before_load_config do
    Rake::Task['s:backup'].execute
    %w{memoization caching facebook campaign_monitor delayed_job}.each do |switch|
      Rake::Task['s:off'].execute(Rake::TaskArguments.new([:name], [switch]))
    end
  end
  # what to do after db:migrate
  task :after_load_config do
    Rake::Task['s:restore'].execute
    Rake::Task['cache:clear'].execute
  end
end

# make it happen
Rake::Task['db:migrate'].enhance(['db:before_load_config']) do
  Rake::Task['db:after_load_config'].invoke
end

Now my question is: how can I wrap that in a begin/ensure block so the switches are always restored?

Usage

You can do stuff like (in app/models/user.rb):

after_create :subscribe_email if Switches.campaign_monitor?
def subscribe_email
  CampaignMonitor.subscribe email
end

Uhh ohh! Campaign Monitor's API is down and you need to shut off those failing after_creates, like, NOW.

production-server-1:/var/www/apps/my_app $ rake s:off[campaign_monitor]
production-server-1:/var/www/apps/my_app $ sudo monit restart all -g my_app
[...]
production-server-2:/var/www/apps/my_app $ rake s:off[campaign_monitor]
production-server-2:/var/www/apps/my_app $ sudo monit restart all -g my_app

Or, even better, do it with cap:

my-macbook:~/my_app $ cap production s:off ARG=campaign_monitor
my-macbook:~/my_app $ cap production mongrel:restart

For another example, let's say you're a developer who doesn't have a self-signed certificate:

my-macbook:~/my_app $ rake s:off[ssl]

Those changes get persisted in config/switches/current.yml.

If you want to see your switches vis-a-vis the defaults:

my-macbook:~/my_app $ rake s:d
--- 
ssl: true => false

And if you want to go back to the defaults:

my-macbook:~/my_app $ rake s:reset

Remember, you should version control config/switches/defaults.yml and ignore config/switches/current.yml.

Rationale

Sometimes you just need an easy way to "turn off" code.