# Propono

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Propono is a [pub/sub](http://en.wikipedia.org/wiki/Publish-subscribe_pattern) 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](https://www.youtube.com/watch?v=ZM3-Gl5DVgM)

```ruby
# On Machine A
Propono::Client.new.listen('some-topic') do |message|
  puts "I just received: #{message}"
end

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

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

## Changes from v1 to v2

Version 2 of Propono changed a few things: 
- We moved from a global interface to a client interface. Rather than calling `publish` and equivalent on `Propono`, you should now initialize a `Propono::Client` and then call everything on that client. This fixes issues with thread safety and global config.
- We have also removed the dependancy on Fog and instead switch to the `sns` and `sqs` mini-gems of `aws-sdk`.
- UDP and TCP support have been removed, and `subscribe_by_post` has been removed.
- We are now using long-polling. This makes Propono **significantly** faster (10-100x).

## Installation

Add this line to your application's Gemfile:

    gem 'propono'

And then execute:

    $ bundle install

## Usage

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.

```ruby
client = Propono::Client.new
client.config.access_key       = "access-key"       # From AWS
client.config.secret_key       = "secret-key"       # From AWS
client.config.queue_region     = "queue-region"     # From AWS

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

```

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

```ruby
client = Propono::Client.new
client.publish('some-topic', "Some string")
client.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.

```ruby
client = Propono::Client.new
client.config.application_name = "application-name" # Something unique to this app.
client.listen('some-topic') do |message|
  # ... Do something interesting with the message
end
```
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.

### Configuration

The following configuration settings are available:

```
Propono::Client.new 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.logger = "A logger such as Log4r or Rails.logger"

  config.max_retries = "The number of retries if a message raises an exception before being placed on the failed queue"
  config.num_messages_per_poll = "The number of messages retrieved per poll to SQS"
end
```

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

### Is it any good?

[Yes.](http://news.ycombinator.com/item?id=3067434)

## Contributing

Firstly, thank you!! :heart::sparkling_heart::heart:

We'd love to have you involved. Please read our [contributing guide](https://github.com/iHiD/propono/tree/master/CONTRIBUTING.md) for information on how to get stuck in.

### Contributors

This project is managed by the [Jeremy Walker](http://ihid.co.uk).

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

- [Jeremy Walker](https://github.com/iHiD)
- [Malcolm Landon](https://github.com/malcyL)
- [Charles Care](https://github.com/ccare)
- [Rob Styles](https://github.com/mmmmmrob)

## Licence

Copyright (C) 2017 Jeremy Walker

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 [LICENCE.md](https://github.com/iHiD/propono/blob/master/LICENCE.md)
along with this program.