Exchanges

Direct Exchange

How It Works

1. A queue is bound to a direct exchange with a routing key.
2. The direct exchange routes a received message to the bound queue whose routing key is matched.

Routing

Based on a routing key matching

Scenario

Unicast routing

Example

Figure 1 Example direct exchange

As shown in this chart, Message A will be sent to Queue 1 and Queue 2. Message B will be sent to Queue 3.

Fanout Exchange

How It Works

A fanout exchange bound with multiple queues routes received messages to each queue. Fanout exchanges forward messages faster than other exchanges.

Routing

The fanout exchange delivers messages to all bound queues.

Scenario

Broadcast routing

Example

Figure 2 Example fanout exchange

As shown in this chart, Message A will be sent to Queue 1 and Queue 2.

Topic Exchange

How It Works

1. A queue is bound to a topic exchange with a routing key that includes a wildcard.
2. The topic exchange routes a received message to the queue if the message's routing key wildcard is matched.

Supported wildcards are stars (*) and hashes (#). Separate wildcards and words by periods (.), for example, test.#.

• * matches one word.
• # matches zero or more words.

Routing

Based on a routing key wildcard matching

Scenario

Multicast routing

Example

Figure 3 Example topic exchange

As shown in this chart, Message A will be sent to Queue 1 and Queue 2, Message B to Queue 1, Queue 2, and Queue 3, and Message C to Queue 3.

Headers Exchange

How It Works

1. A queue is bound to a headers exchange with a binding expressed in a key-value pair.
2. The headers exchange routes a message to the queue if the binding matches the message's key-value header.

The matching algorithm uses a specific binding key-value pair, which is x-match. Values:

• all: Messages are routed only when all header pairs match.
• any: Messages are routed when any header pair matches.

Routing

Based on matching between key-value pairs in the message headers and the binding (a key-value pair)

Example

Figure 4 Example headers exchange

As shown in this chart, Message A will be sent to Queue 1 and Queue 2, and Message B to Queue 2.