This document describes the concept, types, and usage of exchange in TDMQ for RabbitMQ.
Concept
Exchange is a message routing agent in TDMQ for RabbitMQ. A producer sends a message to an exchange, which then routes the message to one or more queues based on its attributes or content (or discards it). Then, a consumer pulls it from such queues for consumption.
TDMQ for RabbitMQ currently supports four types of exchange: Direct, Fanout, Topic, and Header.
Direct: a direct exchange will route messages to the queue whose binding key exactly matches the routing key.
Fanout: a fanout exchange will route messages to all queues bound to it.
Topic: a topic exchange supports multi-condition match and fuzzy match; that is, it will route messages to the queues bound to it by using routing key pattern match and string comparison.
Header: A header exchange has nothing to do with routing key and matches messages by the Headers attribute. When binding a queue to a header exchange, declare a map key-value pair to implement the binding.
Direct Exchange
Routing rule: a direct exchange will route messages to the queue whose binding key exactly matches the routing key.
Use case: this type of exchange is suitable for filtering messages by simple character identifiers and is often used for unicast routing.
Example:
Message
Routing Key
Binding Key
Queue
Message 1
bizA
bizA
Queue 1
Message 2
bizB
bizB
Queue 2
Fanout Exchange
Routing rule: this type of exchange will route messages to all queues bound to it.
Use case: this type of exchange is suitable for broadcast message scenarios. For example, a distribution system can use a fanout exchange to broadcast various status and configuration updates.
Example
Message
Routing Key
Binding Key
Queue
Message 1
bazA.wechat_pay
bazA.credit, bazB.credit
Queue 1, Queue 2
Message 2
bazA.alipay
bazA.credit, bazB.credit
Queue 1, Queue 2
Message 3
bazC.credit
bazA.credit, bazB.credit
Queue 1, Queue 2
Topic Exchange
Routing rule: this type of exchange supports multi-condition match and fuzzy match; that is, it will route messages to the queues bound to it by using routing key pattern match and string comparison.
The wildcards supported by topic exchanges include asterisk "*" and pound sign "#".
"*" represents a word, such as sh.
"#" represents zero, one, or more words separated by period ".", such as cn.hz.
Use case
This type of exchange is often used for multicast routing. For example, you can use a topic exchange to distribute data about specific geographic locations.
Example
Message
Routing Key
Binding Key
Queue
Message 1
cn.hz
cn.hz.#
Queue 1
Message 2
cn.hz.store
cn.hz.#, cn.*.store
Queue 1, Queue 2
Message 3
cn.sz.store
cn.*.store
Queue 2
Header Exchange
A header exchange has nothing to do with routing key and matches messages by the Headers attribute. When binding a queue to a header exchange, declare a map key-value pair to implement the binding. When a message is sent to RabbitMQ, the Headers attribute of the message will be obtained to match the key-value pair specified during exchange binding, and the message will be routed to the queue only if there is a full match.
The x-match rule has two types:
x-match = all: A message can be received only if all key-value pairs are matched.
x-match = any: A message can be received as long as any key-value pair is matched.
