Dispatch rider is a pub/sub kind of library that allows you to publish a message to a notification system (like Amazon SNS) and then you can subscribe to the channels that you subscribed to and start handling the messages.
Add this line to your application's Gemfile:
gem 'dispatch-rider'
And then execute:
$ bundle
Or install it yourself as:
$ gem install dispatch-rider
Setting up a publisher is simple.
All configuration can be loaded from a hash instead of being done like the examples below. (currently only implemented for the publisher)
eg:
publisher = DispatchRider::Publisher.new
publisher.configure({
notification_services: {
file_system: {}
},
destinations: {
file_foo: {
service: :file_system,
channel: :foo,
options: {
path: "test/channel",
}
}
}
})You can load this configuration hash from a YAML file or something, whatever works well for your environment.
To publish using the filesystem register the path where to publish the message files.
publisher = DispatchRider::Publisher.new
publisher.register_notification_service(:file_system)
publisher.register_destination(:local_message_queue, :file_system, :dev_channel, :path => "tmp/news-updates")
publisher.publish(:destinations => :local_message_queue, :message => {
:subject => "read_news",
:body => {"headlines" => [
"April 29, 2013: Rails 4.0.0.rc1 is released.",
"May 14, 2013: Ruby 2.0.0-p195 is released"
]
}})To publish using AWS::SNS make sure AWS.config has been setup.
It's then as easy as providing the configuration details of the topic to the publisher.
publisher = DispatchRider::Publisher.new
publisher.register_notification_service(:aws_sns)
publisher.register_destination(:sns_message_queue, :aws_sns, :dev_channel, {
:account => 777,
:region => 'us-east-1',
:topic => 'RoR'
})
publisher.publish(:destinations => :sns_message_queue, :message => {
:subject => "read_news",
:body => {"headlines" => [
"April 29, 2013: Rails 4.0.0.rc1 is released.",
"May 14, 2013: Ruby 2.0.0-p195 is released"
]
}})To publish to multiple destinations:
publisher.publish(:destinations => [:local_message_queue, :sns_message_queue], :message => {
:subject => "read_news",
:body => {"headlines" => [
"April 29, 2013: Rails 4.0.0.rc1 is released.",
"May 14, 2013: Ruby 2.0.0-p195 is released"
]
}})Sample Rails publisher:
# app/publishers/news_update
class NewsPublisher
@publisher = DispatchRider::Publisher.new
amazon_config = YAML.load_file("#{Rails.root}/config/amazon.yml")
@publisher.register_notification_service(:aws_sns)
@publisher.register_destination(:sns_message_queue, :aws_sns, :dev_channel, {
:account => amazon_config[:account],
:region => amazon_config[:region],
:topic => "news-updates-#{Rails.env}"
})
@destinations = [:sns_message_queue]
class << self
attr_reader :publisher
attr_accessor :destinations
end
delegate :publisher, :destinations, :to => :"self.class"
def initialize(news)
@news = news
end
def publish
publisher.publish(:destinations => destinations, :message => {
:subject => "read_news",
:body => {"headlines" => @news.headlines}
})
end
end
# app/models/news
class News
serialize :headlines, Array
after_create :publish
def publish
NewsPublisher.new(self).publish
end
end
News.create!(:headlines => [
"April 29, 2013: Rails 4.0.0.rc1 is released.",
"May 14, 2013: Ruby 2.0.0-p195 is released"
])To setup a subscriber you'll need message handlers. The handlers are named the same as the message subjects.
Sample message handler:
# app/handlers/bar_handler
module ReadNews
class << self
def process(message_body)
message_body["headlines"].each do |headline|
puts headline
end
end
end
endSample subscriber setup:
subscriber = DispatchRider::Subscriber.new
subscriber.register_queue(:aws_sqs, :name => "news-updates")
subscriber.register_handler(:read_news)
subscriber.setup_demultiplexer(:aws_sqs)
subscriber.processSample subscriber dispatch error handling (optional):
# using blocks
subscriber.on_dispatch_error do |message, exception|
# put your error handling code here
return false # or return true to permanently remove the message
end
# using methods
def handle_dispatch_error(message, exception)
# put your error handling code here
return false # or return true to permanently remove the message
end
subscriber.on_dispatch_error &method(:handle_dispatch_error)Sample Rails application rake task:
# lib/tasks/dispatch-rider
namespace :"dispatch-rider" do
desc "Tells DispatchRider to start running"
task :run => [:"run:remote"]
namespace :run do
desc "Tells DispatchRider to start running"
task :remote => [:ready, :set_aws_sqs_queue, :process]
desc "Tells DispatchRider to start running (using the filesystem as the queue)"
task :local => [:ready, :set_local_queue, :process]
task :ready => :environment do
puts "Creating subscriber..."
@subscriber = DispatchRider::Subscriber.new
[ # list of message handlers
:read_news
].each do |handler_name|
puts "Registering #{handler_name} handler..."
@subscriber.register_handler(handler_name)
end
end
task :set_aws_sqs_queue do
queue_name = "news-updates-#{Rails.env}"
puts "Setting AWS::SQS #{queue_name} queue..."
@subscriber.register_queue(:aws_sqs, :name => queue_name)
@subscriber.setup_demultiplexer(:aws_sqs)
end
task :set_local_queue do
queue_path = "tmp/news-updates-#{Rails.env}"
puts "Setting local filesystem queue @ #{queue_path.inspect}..."
@subscriber.register_queue(:file_system, :path => queue_path)
@subscriber.setup_demultiplexer(:file_system)
end
task :process do
puts "Running..."
@subscriber.process
end
end
endTo run the subscriber simply execute following:
$ bundle exec rake dispatch-rider:run
To run locally:
$ bundle exec rake dispatch-rider:run:local
- Fork it
- Create your feature branch (
git checkout -b my-new-feature) - Commit your changes (
git commit -am 'Add some feature') - Push to the branch (
git push origin my-new-feature) - Create new Pull Request
Copyright (c) 2013 Suman Mukherjee
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