Promiscuous

Promiscuous is a pub-sub framework for easily replicating data across your Ruby applications. Promiscuous guarantees that a subscriber never sees out of order updates and that all updates are eventually replicated.

Benefits over database replication

• Hetrogenous replication. e.g. replicate from Mongo -> Postgres | ElasticSearch | Redis ...
• "Remote observers". The ability to observe model changes in one application from another.
• Publish virtual attributes

We need a few things for the promiscuous tutorial:

• The AMQP broker RabbitMQ up and running.
• The key-value storage system Redis (at least 2.6) up and running.
• Two Rails applications with the promiscuous gem installed.
• Both applications must be running on separate databases.
• Both applications must have a User model (ActiveRecord or Mongoid) with two attributes name and email.

By including the Promiscuous publisher mixin, we can publish the model attributes:

# app/models/user.rb on the publisher app
class User
  include Promiscuous::Publisher
  publish :name, :email
end

Similarly to the publisher app, we can subscribe to the attributes:

# app/models/user.rb on the subscriber app
class User
  include Promiscuous::Subscriber
  subscribe :name, :email

  after_create { Rails.logger.info "Hi #{name}!" }
end

The subscriber must listen for new data to arrive. Promiscuous has a worker that we can launch with the following command:

bundle exec promiscuous subscribe

You should start the subscriber first, otherwise the appropriate queues will not be created. From now on, you should see the queue in the RabbitMQ web admin page. Create a new user in the publisher's Rails console with:

User.create(:name => 'Yoda')`

You should see the message "Hi Yoda!" appearing in the log file of the subscriber.

• Attributes
• Ephemerals & Observers
• Polymorphism
• Embedded Documents
• Foreign Keys
• Namespace Mapping
• Promiscuous DSL

• Configuration Options
• Subscriber CLI Options

• Exporting Publishers Definitions
• Unit Testing
• Integration Testing
• Gemify your Apps

• RabbitMQ & Redis
• Initial Sync
• Error Handling
• Instrumentation
• Managing Deploys
• Setup with Unicorn, Resque, etc.

• Roadmap
• Coding Restrictions
• Limitations
• FAQs
• License