A pub/sub architecture as Ruby Gem

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Propono is a pub/sub gem built on top of Amazon Web Services (AWS). It uses Simple Notification Service (SNS) and Simple Queue Service (SQS) to seamlessly pass messages throughout your infrastructure.

It's beautifully simple to use. Watch an introduction

# On Machine A
Propono.listen_to_queue('some-topic') do |message|
  puts "I just received: #{message}"

# On Machine B
Propono.publish('some-topic', "The Best Message Ever")

# Output on Machine A a second later.
# - "I just received The Best Message Ever"


Add this line to your application's Gemfile:

gem 'propono'

And then execute:

$ bundle install


The first thing to do is setup some configuration keys for Propono. It's best to do this in an initializer, or at the start of your application.

Propono.config.access_key       = "access-key"       # From AWS
Propono.config.secret_key       = "secret-key"       # From AWS
Propono.config.queue_region     = "queue-region"     # From AWS

# Or use the IAM profile of the machine
Propono.config.use_iam_profile  = true
Propono.config.queue_region     = "queue-region"     # From AWS

You can then start publishing messages easily from anywhere in your codebase.

Propono.publish('some-topic', "Some string")
Propono.publish('some-topic', {some: ['hash', 'or', 'array']})

Listening for messages is easy too. Just tell Propono what your application is called and start listening. You'll get a block yielded for each message.

Propono.config.application_name = "application-name" # Something unique to this app.
Propono.listen_to_queue('some-topic') do |message|
  # ... Do something interesting with the message

In the background, Propono is automatically setting up a queue using SQS, a notification system using SNS, and gluing them all together for you. But you don't have to worry about any of that.

Does it matter what I set my application_name to? For a simple publisher and subscriber deployment, no. However, the application_name has a direct impact on subscriber behaviour when more than one is in play. This is because a queue is established for each application_name/topic combination. In practice:

  • subscribers that share the same application_name will act as multiple workers on the same queue. Only one will get to process each message.
  • subscribers that have a different application_name will each get a copy of a message to process independently i.e. acts as a one-to-many broadcast.

Note for using in Rake tasks and similar: Propono spawns new threads for messages sent via SNS. If your application ends before the final thread is executed, then the last message might not send. There are two options to help you here:

  • Pass the {async: false} option to Propono.publish. (This was introduced in 1.3.0)
  • Do a Thread#join on each thread that is returned from calls to publish.

 Using TCP for messages

Publishing directly to SNS takes about 15x longer than publishing over a simple TCP connection. It is therefore sometimes favourable to publish to a separate machine listening for TCP messages, which will then proxy them on.

To send messages this way, you need to set up a little extra config:

Propono.config.tcp_host = ""
Propono.config.tcp_port = 12543

You then simply pass the :tcp protocol into publish

Propono.publish('some-topic', message, protocol: :tcp)

You'll now need another application running Propono to listen to the TCP feed. You can use the same machine or a different one, just make sure the port config is the same in both applications, and you're good to go.

Propono.listen_to_tcp do |topic, message|
  Propono.publish(topic, message) # Proxy the message to SNS

This proxying of TCP to SQS is used so often that there's a simple shortcut. Just run this on the machine receiving the TCP packets.


 Using UDP for messages

If you want almost-zero performance impact, and don't mind the occasional message getting lost, you can use UDP. We use this for things like our live dashboard where we don't mind losing a piece of activity here and there, but any performance impact on our Meducation itself is bad news.

Sending messages in this way is very similar to using TCP. First add some config:

Propono.config.udp_host = ""
Propono.config.udp_port = 12543

You then simply pass the :udp protocol into publish:

Propono.publish('some-topic', message, protocol: :udp)

As per the listen_to_tcp method explained above, you now listen to UDP or use the proxy method:

Propono.listen_to_udp do |topic, message|
  Propono.publish(topic, message) # Proxy the message to SNS



The following configuration settings are available:

Propono.config do |config|
  # Use AWS access and secret keys
  config.access_key = "An AWS access key"
  config.secret_key = "A AWS secret key"
  # Or use AWS IAM profile of the machine
  config.use_iam_profile = true

  config.queue_region = "An AWS queue region"
  config.application_name = "A name unique in your network"
  config.udp_host = "The host of a machine used for UDP proxying"
  config.udp_port = "The port of a machine used for UDP proxying"
  config.tcp_host = "The host of a machine used for TCP proxying"
  config.tcp_port = "The port of a machine used for TCP proxying"
  config.logger = "A logger such as Log4r or Rails.logger"

These can all also be set using the Propono.config.access_key = "..." syntax.

Is it any good?



Firstly, thank you!! ❤️💖❤️

We'd love to have you involved. Please read our contributing guide for information on how to get stuck in.


This project is managed by the Meducation team.

These individuals have come up with the ideas and written the code that made this possible:


Copyright (C) 2015 New Media Education Ltd

This program is free software: you can redistribute it and/or modify it under the terms of the MIT License.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the MIT License for more details.

A copy of the MIT License is available in along with this program.