RabbitMQ

AMQP messaging solution ideal for IoT and client/server use cases

Overview

RabbitMQ is lightweight and easy to deploy messaging platform. It supports multiple messaging protocols. RabbitMQ can be deployed in distributed and federated configurations to meet high-scale, high-availability requirements. Joule provides the ability to consume events using RabbitMQ messaging subscription

Client library: com.rabbitmq:amqp-client:5.16.0

Example

This example configures a RabbitMQ consumer to receive three event types using the routing keys elements from the topic exchange type. Quote events are deserialised from a StreamEvent Json object to a Joule StreamEvent object.

rabbitConsumer:
  host: localhost
  exchange:
    name: marketQuotes
    type: TOPIC
  
  routing:
    keys:
      - NASDAQ.IBM
      - NASDAQ.MSFT
      - NASDAQ.GOOG
  
  deserializer:
    parser: 
      com.fractalworks.examples.banking.data.QuoteToStreamEventParser

Attributes schema

Attribute	Description	Data Type	Required
host	RabbitMQ server hostname or Ip address	String Default: localhost
port	RabbitNQ server port, must be greater than 0.	Integer Default: 5672
username	User name	String Default: guest
password	password	String Default: guest
virtualHost	Creates a logical group of connections, exchanges, queues, bindings, user permissions, etc. within an instance. See vhost documentation for further information	String Default: /
autoAck	Flag to consider if server should message acknowledged once messages have been delivered. False will provide explicit message acknowledgment.	Boolean Default: true
prefetchCount	QoS -maximum number of messages that the server will deliver, 0 if unlimited	Integer Default: 1
global	QoS - true if the settings should be applied to the entire channel rather than each consumer	Boolean Default: true
durable	Set a durable queue (queue will survive a server restart)	Boolean Default: true
autoDelete	Server deletes queue when not in use	Boolean Default: true
exclusive	Exclusive queue to this connection	Boolean Default: false
arguments	Additional queue properties	Map<String, Object> Default: null
exchange	Exchange configuration	See Exchange Attributes section
routing	Routing configuration	See Routing Attributes section
deserializer	Deserialization configuration	See Deserialization documentation

Exchange Attributes

Attribute	Description	Data Type	Required
name	Name of exchange	String
type	In RabbitMQ, messages are published to an exchange and, depending on the type of exchange, the message gets routed to one or more queues.	TOPIC, DIRECT, FANOUT, HEADERS Default: TOPIC
arguments	Additional binding properties	Map<String, Object> Default: null

Exchange example

exchange:
    name: marketQuotes
    type: DIRECT

Routing Attributes

Attribute	Description	Data Type	Required
keys	Consumers can selectively consume events sent to a topic exchange by specifying one or more words delimited by dots. Valid key format examples: 'nasdaq.ibm', 'dept.inventory.bolts'. There are two important special cases to define keys. (star) can be substituted for exactly one word #(hash) can be substituted for zero or more words	String Default: All Constraints: Any number of dot separated word to a limit of 255 bytes

Routing example

This example will subscribe to all events that match the first component of the key 'NASDAQ'

  routing:
    keys:
      - NASDAQ.#

---

Further examples

All examples assume default values when not applied.

Queue based eventing

Sets up a simple consumer which subscribes to events directly off of a queue.

rabbitConsumer:
  queue: point_to_point_queue
  ...

Work Queues

Subscribe to a Worker Queue that is used to distribute time-consuming tasks among multiple Joule workers.

rabbitConsumer:
  queue: worker_queue
  autoAck: false
  durable: true
  prefetchCount: 1
  ...

Publish/Subscribe

This example each consumer process will receive the same message. Because the exchange is configured as a fanout we do not need to use the routing element, this will be covered in the next example

rabbitConsumer:
  exchange:
    name: quotes_exchange
    type: FANOUT    
  ...

Routing

This time we're going to make it possible to subscribe only to a subset of the messages for a single consumer. Therefore each Joule consumer process will have its own routing keys they would subscribe to. In the case below a process using this configuration will only receive IBM and MSFT quotes.

rabbitConsumer:
  host: localhost
  exchange:
    name: quotes_exchange
    type: DIRECT

  routing:
    keys:
      - NASDAQ.IBM
      - NASDAQ.MSFT
  ...

Topic

This example is very similar to the previous case whereby we subscribe to events that we are interested in. However, we are using a topic exchange that enabled us to use the dot notation and wildcards to subscribe to a wider set of events. In the case below we would receive all market venue quotes for both IBM and MSFT.

rabbitConsumer:
  host: localhost
  exchange:
    name: quotes_exchange
    type: TOPIC

  routing:
    keys:
      - "*.IBM"
      - "*.MSFT"
  ...

Additional Resources

Further AMQP resources can be found on the following links:

• Official RabbitMQ documentation

• CloudAMQP documentation