switches

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

It’s an extraction from 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/zzz_rake_switches.rake:

namespace :rake_switches do
  task :turn_stuff_off 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
  task :turn_stuff_back_on do
    Rake::Task['s:restore'].execute
    Rake::Task['cache:clear'].execute
  end
end

# modify what happens on db:migrate, etc.
[ 'db:migrate', 'your:task:if:it:needs:wrapping' ].each do |task_to_wrap|
  Rake::Task[task_to_wrap].enhance(['rake_switches:turn_stuff_off']) do
    Rake::Task['rake_switches:turn_stuff_back_on'].invoke
  end
end

Note that ‘s:backup’ and ‘s:restore’ are not thread safe or really GFS safe, either.

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.

switches

Quick start

Tasks

Throwing switches remotely with Capistrano

Throwing switches before you db:migrate

Usage

Rationale

Wishlist

Copyright