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RabbitMQ Introduced in Brief

by TheDailyTechTalkSeptember 17th, 2021

Too Long; Didn't Read

RabbitMQ is an open source message broker software sometimes called message-oriented middleware. RabbitMq is used to distribute long-running task that doesn’t require immediate user feedback into a separate process. RabbitMQ has 5 different exchanges: Direct exchange, Fanout exchange, Header exchange, Dead Letter exchange and Dead Letter Exchange. The RabbitMQ topology is similar to a direct one - a message sent directly to a topic exchange with a particular key that will be delivered to all of the queues that are bound to it.

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In this blog post, we are going to cover an overview of what RabbitMQ is and give an example of when you would apply this technology.

What is RabbitMQ?

RabbitMq is an open source message broker software. sometimes called message-oriented middleware, that originally implemented the Advanced Message Queuing Protocol or >AMQp for short, and has since been extended with a plug-in architecture to support Streaming Text Oriented Messaging Protocol (STOMP), Message Queuing Telemetry >Transport (MQTT), and other protocols.

The simplest way of putting it would be RabbitMQ is used to distribute long-running task that doesn’t require immediate user feedback into a separate process.

Now since we have a good understanding of the definition let’s dive deep into the components of RabbitMq, its topology, and how we can use it.

RabbitMq has 5 different exchanges:

Direct exchange
Fanout exchange
Header exchange
Dead Letter exchange
Topic exchange

Basic components of RabbitMq

Exchanges

Exchange	Description
Direct	Direct exchange delivers messages to queues based on a message routing key.
Fanout	Fanout exchange routes messages to all of the queues that are bound to it and the routing key is ignored.
Header	Headers exchange routes messages based on arguments containing headers and optional values. Headers exchanges are very similar to topic exchanges, but route messages based on header values instead of routing keys.
Dead Letter Exchange	Provides the functionality to capture messages that are not deliverable.
Topic	Topic exchanges route messages to queues based on wildcard matches between the routing key and the routing pattern, which is specified by the queue binding. Messages are routed to one or many queues based on a matching between a message routing key and this pattern.

Components

Exchange	Description
Binding	Binding is a “link” that you set up to bind a queue to an exchange.
Routing key	Routing key The routing key is a message attribute. The exchange might look at this key when deciding how to route the message to queues (depending on exchange type).
Producers	Job of the producer is to send a new message to the exchange.
Message	Message represents value you want the consumer to recieve and process.
Queue	Queues are ordered collections of messages.
Exchange	Exchange routes the message to the right queue.
Consumers	Consumers is a client that receives messages.

Direct exchange

A direct exchange delivers messages to queues based on a message routing key. The routing key is a message attribute added to the message header by the producer. Think of the routing key as an "address" that the exchange is using to decide how to route the message. A message goes to the queue(s) with the binding key that exactly matches the routing key of the message.

Fanout exchange

A fan-out topology is when the producer sends a message to the exchange and the exchanges ignore the routing key and just sends the task directly to all of the queues that are available.

Topic exchange

The logic behind the topic exchange is similar to a direct one - a message sent with a particular routing key will be delivered to all the queues that are bound with a matching binding key. There are two important special cases for binding keys:

* can substitute for exactly one word.
# can substitute for zero or more words.

Dead Letter exchange

There are three identified situations where a message becomes undeliverable after reaching RabbitMQ:

A message is negatively acknowledged by the consumer
The TTL of a message expires
The queue reaches capacity

By default, the broker drops these messages. Publishing is successful, however, the RabbitMQ consumer never handles or has a chance to handle the message successfully.

Queues attached to a dead letter exchange collect dropped messages, with the next steps determined by the developer. In other words - it's up to you to decide how to handle messages in the dead letter queue. When implemented correctly, information is almost never lost.

Header exchange

Headers exchange is an exchange which route messages to queues based on message header values instead of routing key. Producer adds some values in a form of key-value pair in message header and sends it to headers exchange. After receiving a message, exchange try to match all or any (based on the value of “x-match”) header value with the binding value of all the queues bound to it.

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