RabbitMQ has a few different types of exchanges.

• Direct Exchange
• Fanout Exchange
• Header Exchange
• Topic Exchange

A header exchange uses headers instead of routing keys to determine where a message should be routed. For example, let's say there is a header exchange named header.exchange and a queue named header.queue. In this scenario, header.exchange could be bound to header.queue with the following arguments.

• foo = bar
• x-match = any or x-match = all

AVOID TROUBLE

Only simple key value pairs can be used. Complex keys, such as a nested or multidimensional key will fail to match.

Now let's say a message is published to header.exchange with header foo = bar.

In this scenario, since header.exchange is bound to header.queue with argument foo = bar, the message should be routed from header.exchange to header.queue.

A messages headers can be seen using the RabbitMQ REST API. In this example, the messages in header.queue in the foo virtual host will be returned.

curl 
--request POST 
--user john.doe:itsasecret 
--data '{"count":1,"ackmode":"ack_requeue_true","encoding":"auto","truncate":0}'
--url http://server001:15671/api/queues/foo/header.queue/get

The output should look something like this. Notice there is a header where the key is "foo" and the value is "bar".

[
    {
        "exchange": "header.exchange",
        "message_count": 0,
        "payload": "Hello World",
        "payload_bytes": 11,
        "payload_encoding": "string",
        "properties": {
            "delivery_mode": 2,
            "headers": {
                "foo": "bar",
                "timestamp_in_ms": 1637208962854
            },
            "timestamp": 1637208962
        },
        "redelivered": false,
        "routing_key": ""
    }
]