RabbitMQ adapter for Yggdrasil

This project is a RabbitMQ adapter for Yggdrasil publisher/subscriber.

Small example

The following example uses RabbitMQ adapter to distribute messages:

iex(1)> channel = %Yggdrasil.Channel{
iex(1)>   name: {"amq.topic", "some_channel"},
iex(1)>   adapter: :rabbitmq
iex(1)> }
iex(2)> Yggdrasil.subscribe(channel)
iex(3)> flush()
{:Y_CONNECTED, %Yggdrasil.Channel{(...)}}

and to publish a message for the subscribers:

iex(4)> Yggdrasil.publish(channel, "message")
iex(5)> flush()
{:Y_EVENT, %Yggdrasil.Channel{(...)}, "message"}

When the subscriber wants to stop receiving messages, then it can unsubscribe from the channel:

iex(6)> Yggdrasil.unsubscribe(channel)
iex(7)> flush()
{:Y_DISCONNECTED, %Yggdrasil.Channel{(...)}}

RabbitMQ adapter

The RabbitMQ adapter has the following rules:

• The adapter name is identified by the atom :rabbitmq.
• The channel name must be a tuple with the exchange and the routing key.
• The transformer must encode to a string. From the transformers provided it defaults to :default, but :json can also be used.
• Any backend can be used (by default is :default).

The following is an example of a valid channel for both publishers and subscribers:

%Yggdrasil.Channel{
  name: {"amq.topic", "postgres_channel_name"},
  adapter: :rabbitmq,
  transformer: :json
}

It will expect valid JSONs from RabbitMQ and it will write valid JSONs in RabbitMQ.

RabbitMQ configuration

Uses the list of options for AMQP, but the more relevant optuons are shown below:

• hostname - RabbitMQ hostname (defaults to "localhost").
• port - RabbitMQ port (defaults to 5672).
• username - RabbitMQ username (defaults to "guest").
• password - RabbitMQ password (defaults to "guest").
• virtual_host - Virtual host (defaults to "/").
• heartbeat - Heartbeat of the connections (defaults to 10 seconds).
• subscriber_options - Controls the amount of connections established with RabbitMQ. These are poolboy options for RabbitMQ subscriber (defaults to [size: 5, max_overflow: 10]).

The following shows a configuration with and without namespace:

# Without namespace
config :yggdrasil,
  rabbitmq: [hostname: "rabbitmq.zero"]

# With namespace
config :yggdrasil, RabbitMQOne,
  postgres: [
    hostname: "rabbitmq.one",
    port: 1234
  ]

Also the options can be provided as OS environment variables. The available variables are:

• YGGDRASIL_RABBITMQ_HOSTNAME or <NAMESPACE>_YGGDRASIL_RABBITMQ_HOSTNAME.
• YGGDRASIL_RABBITMQ_PORT or <NAMESPACE>_YGGDRASIL_RABBITMQ_PORT.
• YGGDRASIL_RABBITMQ_USERNAME or <NAMESPACE>_YGGDRASIL_RABBITMQ_USERNAME.
• YGGDRASIL_RABBITMQ_PASSWORD or <NAMESPACE>_YGGDRASIL_RABBITMQ_PASSWORD.
• YGGDRASIL_RABBITMQ_VIRTUAL_HOST or <NAMESPACE>_YGGDRASIL_RABBITMQ_VIRTUAL_HOST.
• YGGDRASIL_RABBITMQ_HEARTBEAT or <NAMESPACE>_YGGDRASIL_RABBITMQ_HEARTBEAT.

where <NAMESPACE> is the snakecase of the namespace chosen e.g. for the namespace RabbitmqTwo, you would use RABBITMQ_TWO as namespace in the OS environment variable.

Installation

Using this RabbitMQ adapter with Yggdrasil is a matter of adding the available hex package to your mix.exs file e.g:

def deps do
  [{:yggdrasil_rabbitmq, "~> 4.1"}]
end

Running the tests

A docker-compose.yml file is provided with the project. If you don't have a RabbitMQ database, but you do have Docker installed, then just do:

$ docker-compose up --build

And in another shell run:

$ mix deps.get
$ mix test

Relevant projects used

• AMQP: AMQP application.
• Connection: wrapper over GenServer to handle connections.

Author

Alexander de Sousa.

License

Yggdrasil is released under the MIT License. See the LICENSE file for further details.