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A broker is a component that acts as the intermediary in a messaging system. Here, the clients connect to the broker and not to each other directly. Whenever clients want to send and receive messages, they need to specify a mailbox/topic/queue on the broker. Producers connect to the broker and send messages to a specific queue. Consumers connect to the broker and specify queue name from which they want to read messages.
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Responsabilities
- Maintaining the mapping of queues, producers, and consumers reliably: This includes storing the messages in a durable format
- Handling message production: This includes storing messages written by the producers.
- Handling message consumption: This means ensuring that consumers reliably get messages and providing constructs to avoid duplicate messages
- Routing and transformation: Here, the message broker may transform or maintain multiple copies for each message to enable various topology models, which will be described in the following sections.
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Models
- Queue
- Pub/Sub