Mantle

To learn more about Mantle and it's internal, see this slide deck.

Installation

Add this line to your application's Gemfile:

gem 'mantle'

or install manually by:

$ gem install mantle

Usage (in Rails App)

Setup a Rails initializer(config/initializers/mantle.rb):

Mantle.configure do |config|
  config.message_bus_redis = Redis.new(host: ENV["MESSAGE_BUS_REDIS_URL"] || 'localhost')
  config.message_handlers = {
    'account:update' => 'MyMessageHandler',
    'order' => ['MyMessageHandler', 'MyOtherMessageHandler']
  }
end

The config takes a number of options, many of which have defaults:

Mantle.configure do |config|
  config.message_bus_redis = Redis.new(host: 'localhost') # default: localhost
  config.logger = Rails.logger # default: Logger.new(STDOUT)
  config.redis_namespace = "my-namespace" # default: no namespace
  config.message_handlers = {'deal:update' => 'MyHandler'} # default: {}
end

To make the installation of mantle easier, the following command will create these files in a Rails application:

$ rails g mantle:install

If an application only pushes messages on to the queue and doesn't listen, the following configuration is all that's needed:

Mantle.configure do |config|
  config.message_bus_redis = Redis.new(host: 'localhost') # default: localhost
  config.logger = Rails.logger # default: Logger.new(STDOUT)
end

Publish messages to consumers:

Mantle::Message.new("person:create").publish({ id: message['id'], data: message['data'] })

The first and only argument to Mantle::Message.new is the channel you want to publish the message on. The #publish method takes the message payload (in any format you like) and pushes the message on to the message bus pub/sub and also adds it to the catch up queue so offline applications can process the message when they become available.

Define message handler class with .receive method. For example app/models/my_message_handler.rb

class MyMessageHandler
  def self.receive(channel, message)
    puts channel # => 'order'
    puts message # => { 'id' => 5, 'name' => 'Brandon' }
  end
end

To run the listener:

$ bin/mantle

or with configuration:

$ bin/mantle -c ./config/initializers/other_file.rb

To run the processor:

$ bin/sidekiq -q mantle

If the Sidekiq worker should also listen on another queue, add that to the command with:

$ bin/sidekiq -q mantle -q default

It will NOT add the default queue to processing if there are other queues enumerated using the -q option.

Testing

Requiring this library causes messages to be appended to an in-memory array.

# test/test_helper.rb
require 'mantle/testing'

class OrderMessage
  def perform(message)
    Mantle::Message.new("order:create").publish(message)
  end
end

class OrderMessageTest < ActiveSupport::TestCase
  test "sends a mantle message on created order" do
    OrderMessage.new.perform(mantle_message)
    assert_equal 1, Mantle.messages.size

    msg = Mantle.messages.first
    assert_equal "order:create", msg.channel
    assert_equal mantle_message, msg.message
  end

  private

  def mantle_message
    { id: 5 }
  end
end

Be sure to clear out messages so they don't build up during the test suite:

def teardown
  Mantle.clear_all
end