ConduitAMQP

An AMQP adapter for Conduit.

Installation

This package can be installed as:

1. Add conduit_amqp to your list of dependencies in mix.exs:

   def deps do
     [{:conduit_amqp, "~> 0.6.3"}]
   end

2. Ensure conduit_amqp is started before your application:

   def application do
     [applications: [:conduit_amqp]]
   end

Configuring the Adapter

# config/config.exs

config :my_app, MyApp.Broker,
  adapter: ConduitAMQP,
  url: "amqp://my_app:secret@my-rabbit-host.com"

# Stop lager redirecting :error_logger messages
config :lager, :error_logger_redirect, false

# Stop lager removing Logger's :error_logger handler
config :lager, :error_logger_whitelist, [Logger.ErrorHandler]

For the full set of options, see ConduitAQMP.

Configuring Exchanges

You can define exchanges with the exchange macro in the configure block of your Broker. The exchange macro accepts the name of the exchange and options for the exchange.

Options

• :type - Either :topic, :fanout, :direct, or :headers. Defaults to :topic.
• :durable - If set, keeps the Exchange between restarts of the broker. Defaults to false.
• :auto_delete - If set, deletes the Exchange once all queues unbind from it. Defaults to false.
• :passive - If set, returns an error if the Exchange does not already exist. Defaults to false.
• :internal - If set, the exchange may not be used directly by publishers. Defaults to false.

See exchange.declare for more details.

Example

defmodule MyApp.Broker do
  use Conduit.Broker, otp_app: :my_app

  configure do
    exchange "my.topic", type: :topic, durable: true
  end
end

Configuring Queues

You can define queues with the queue macro in the configure block of your Broker. The queue macro accepts the name of the queue and options for the exchange.

Options

• :durable - If set, keeps the Queue between restarts of the broker. Defaults to false.
• :auto_delete - If set, deletes the Queue once all subscribers disconnect. Defaults to false.
• :exclusive - If set, only one subscriber can consume from the Queue. Defaults to false.
• :passive - If set, raises an error unless the queue already exists. Defaults to false.
• :from - A list of routing keys to bind the queue to.
• :exchange - Name of the exchange used to bind the queue to the routing keys.

See queue.declare for more details.

Example

defmodule MyApp.Broker do
  use Conduit.Broker, otp_app: :my_app

  configure do
    queue "my.queue", from: ["#.created.user"], exchange: "amq.topic", durable: true
  end
end

Configuring a Subscriber

Inside an incoming block for a broker, you can define subscriptions to queues. Conduit will route messages on those queues to your subscribers.

defmodule MyApp.Broker do
  incoming MyApp do
    subscribe :my_subscriber, MySubscriber, from: "my.queue"
    subscribe :my_other_subscriber, MyOtherSubscriber,
      from: "my.other.queue",
      prefetch_size: 20
  end
end

Options

• :from - Accepts a string or function that resolves to the queue to consume from. Defaults to the name of the route if not specified.
• :prefetch_size - Size of prefetch buffer in octets. Defaults to 0, which means no specific limit. This can also be configured globally by passing this same option when configuring your Broker.
• :prefetch_count - Number of messages to prefetch. Defaults to 0, which means no specific limit. This can also be configured globally by passing this same option when configuring your Broker.
• :consumer_tag - Specifies the identifier for the consumer. The consumer tag is local to a channel, so two clients can use the same consumer tags. If this field is empty the server will generate a unique tag.
• :no_local - If the no-local field is set the server will not send messages to the connection that published them. Defaults to false.
• :no_ack - If this field is set the server does not expect acknowledgements for messages. That is, when a message is delivered to the client the server assumes the delivery will succeed and immediately dequeues it. Defaults to false.
• :exclusive - Request exclusive consumer access, meaning only this consumer can access the queue. Defaults to false.
• :nowait - If set, the server will not respond to the method. The client should not wait for a reply method. If the server could not complete the method it will raise a channel or connection exception. Defaults to false.
• :arguments - A set of arguments for the consume. Defaults to [].

Note: It's highly recommended to set :prefetch_size or :prefetch_count to a non-zero value to limit the memory consumed when a queue is backed up.

See basic.qos and basic.consume for more details on options.

Configuring a Publisher

Inside an outgoing block for a broker, you can define publications to exchanges. Conduit will deliver messages using the options specified. You can override these options, by passing different options to your broker's publish/3.

defmodule MyApp.Broker do
  outgoing do
    publish :something,
      to: "my.routing_key",
      exchange: "amq.topic"
    publish :something_else,
      to: "my.other.routing_key",
      exchange: "amq.topic"
  end
end

Options

• :to - The routing key for the message. If the message already has it's destination set, this option will be ignored.
• :exchange - The exchange to publish to. This option is required.

See basic.publish for more details.

Architecture

When ConduitAMQP is used as an adapter for Conduit, it starts ConduitAMQP as a child supervisor. ConduitAMQP starts:

1. ConduitAQMP.ConnPool - Creates and supervises a pool of AMQP connections.
2. ConduitAMQP.PubSub - Creates and supervises ConduitAMQP.PubPool and ConduitAMQP.SubPool.
3. ConduitAMQP.Subscribers - A supervisor for subscribers that process messages.