Hello RabbitMQ

This is a sample project to experiment with RabbitMQ.

• Prerequisites
  • RabbitMQ
    • Setup
    • Configuration
  • Application Configuration
• Sending Messages
  • Request Payload
  • Broadcast (Fanout)
  • Topic Message
• Consuming Messages
  • Fanout Messages
  • Topic Messages

Prerequisites

RabbitMQ

This project requires a running RabbitMQ server.

Setup

It can be started on your local machine using docker-compose:

$ docker-compose up -d rabbitmq

Configuration

The applications in this repository use the implicit default configuration for RabbitMQ:

spring:
  rabbitmq:
    host: localhost
    port: 5672
    username: guest
    password: guest
    virtualhost: vhost

If changed, these values need to be set in the application.yml configuration files of the services that are supposed to connect to that RabbitMQ server.

Application Configuration

Both message producer and consumer require configuration of the exchanges to use.

Currently, the support a topic exchange and a fanout exchange:

messaging:
  exchange:
    fanout: as.fanout
    topic: as.topic

These exchanges don’t need to exist before the applications start, i.e., they don’t need to be set up in the Rabbit MQ management interface on port 15672 manually. The applications are able to create them as needed. The same applies to queues and queue bindings.

Sending Messages

The producer service running on port 8080 provides a REST API to send messages to both the fanout exchange as well as the topic exchange.

If the message was sent successfully, the endpoints return a 204 No Content HTTP response.

Request Payload

Both endpoints acccept a request body in JSON format with the following fields:

JSON Field	Description
key	some arbitrary String value, e.g., some identifier of the event that’s being sent as a message
payload	an arbitrary JSON data structure

In fact, the entire JSON structure in the REST request is only relevant for the payload of the Rabbit MQ message, i.e., the specified key has no relevance for the routing. The structure moreover is just an example for a "complex" data structure as message payload.

Broadcast (Fanout)

Broadcast messages are sent to the fanout exchange configured by the property messaging.exchange.fanout.

POST localhost:8080/broadcast

{
  "key": "my-event",
  "payload": {
    "flag": true,
    "count": 4,
    "elements": [
        "value"
    ]
   }
}

Topic Message

Topic messages are sent to the topic exchange configured by the property messaging.exchange.topic.

In addition to the topic, a routing key will be set. It is defined by the routingKey path variable, but also uses the exchange name as a prefix.

POST localhost:8080/send/topic/{routingKey}

{
  "key": "my-event",
  "payload": {
    "flag": true,
    "count": 4,
    "elements": [
        "value"
    ]
   }
}

Consuming Messages

In contrast to the producer, the consumer service uses a random port. This allows for starting several instances of the same service.

Fanout Messages

Each instance of the consumer service creates a Rabbit MQ queue and binds it to the fanout exchange, so that all consumer services instances receive a message.

INFO c.a.h.c.service.ConsumerServiceRabbit    : Received message object on fanout: Event(key=Fanout, payload=Hello World)
INFO c.a.h.c.service.ConsumerServiceRabbit    : Headers: {amqp_receivedDeliveryMode=PERSISTENT, amqp_contentEncoding=UTF-8, amqp_receivedExchange=as.fanout, amqp_deliveryTag=2, amqp_consumerQueue=8d750f5a-5278-4c1d-a4c3-6fcd26cbd50c, amqp_redelivered=false, id=900d424a-633d-3980-a681-30769fad53a0, amqp_consumerTag=amq.ctag-z5TpXftS1oYL0HTszLsGiQ, contentType=application/json, __TypeId__=cc.andreassiegel.hellorabbitmq.common.model.Event, timestamp=1508935384693}

Topic Messages

Different than the individual queues bound to the fanout exchange, all consumer service instances bind to the same queue (log-consumer in this case). With this setup, only one instance of a service receives a particular message from the topic exchange.

In addition to that, message consumption also depends on the routing key, but the current implementation binds to the routing key ${messaging.exchange.topic}.#. Hence, consumers will receive all messages that were sent to the topic exchange with the exchange name as prefix.

INFO c.a.h.c.service.ConsumerServiceRabbit    : Received message object on topic exchange: Event(key=Topic, payload=Hello World)
INFO c.a.h.c.service.ConsumerServiceRabbit    : Headers: {amqp_receivedDeliveryMode=PERSISTENT, amqp_receivedRoutingKey=as.topic.hello.world, amqp_contentEncoding=UTF-8, amqp_receivedExchange=as.topic, amqp_deliveryTag=3, amqp_consumerQueue=log-consumer, amqp_redelivered=false, id=f558aed7-9337-f9da-bbe5-bc9c583a2acf, amqp_consumerTag=amq.ctag-ogyT6TxHCCl1k6sXs3DwOA, contentType=application/json, __TypeId__=cc.andreassiegel.hellorabbitmq.common.model.Event, timestamp=1508935795826}