The X-Death Headers Exchange is a custom RabbitMQ exchange type that extends the standard headers exchange functionality by enabling routing decisions based on the x-death headers. This solves a limitation in RabbitMQ where the standard headers exchange cannot route messages based on death information.

In standard RabbitMQ, when a message is dead-lettered (rejected, expired, or queue exceeded), it accumulates x-death headers containing information about why and where it "died". However, the standard headers exchange doesn't allow routing based on them.

This exchange type removes that limitation. Making it possible to have bindings on x-death information when using all-with-x and any-with-x matchings.

If you're looking for more advanced routing capabilities for more sophisticated DLQ topologies, you might be looking for RADLX (RabbitMQ exchange that enables atomic, per-message death decisions with retries)

1. Download the compatible version from the releases directory
2. Place the .ez file in your RabbitMQ plugins directory
3. Enable the plugin:

rabbitmq-plugins enable rabbitmq_x_death_headers_exchange

For other versions, please create an issue.

When a message with x-death headers arrives to the exchange, the death information is automatically mapped to routable headers with the following pattern:

x-death[<queue_name>][<reason>]-<property> = <value>

For example, if a message was rejected from a queue named "orders", the following headers would be created:

• x-death[orders][rejected]-count = 1
• x-death[orders][rejected]-exchange = "original.exchange"
• x-death[orders][rejected]-routing-keys = "order.created,order.processed"

┌─────────────────┐
│ Original Queue  │
│    "orders"     │
└────────┬────────┘
         │ Message rejected
         ▼
┌─────────────────┐     x-death header:
│  Dead Letter    │     [{
│    Exchange     │       queue: "orders",
│ "x-death-dlx"   │       reason: "rejected",
│                 │       count: 1,
└────────┬────────┘       exchange: "app.exchange",
         │                routing-keys: ["order.new"]
         │              }]
         ▼
┌─────────────────────────────────────────┐
│     X-Death Headers Exchange Maps to:   │
│                                         │
│  x-death[orders][rejected]-count = 1    │
│  x-death[orders][rejected]-exchange =   │
│           "app.exchange"                │
│  x-death[orders][rejected]-routing-keys │
│           = "order.new"                 │
└──────────────┬──────────────────────────┘
               │
               ├─── Binding 1: x-match="all-with-x"
               │    x-death[orders][rejected]-count = 1
               │    ▼
               │    ┌─────────────────┐
               │    │ Retry Queue     │
               │    └─────────────────┘

# Declare the x-death-headers exchange
rabbitmqadmin declare exchange name=dlx type=x-death-headers

# Declare queue1 with dead letter exchange
rabbitmqadmin declare queue name=queue1 arguments='{"x-dead-letter-exchange":"dlx"}'

# Declare queue2 with TTL and dead letter exchange  
rabbitmqadmin declare queue name=queue2 arguments='{"x-message-ttl":1000,"x-dead-letter-exchange":"dlx"}'

# Declare the alarming queue
rabbitmqadmin declare queue name=alarming_queue

# Bind queue2 to dlx for messages that rejected from queue1
rabbitmqadmin declare binding source=dlx destination=queue2 destination_type=queue \
  arguments='{"x-match":"all-with-x","x-death[queue1][rejected]-count":1}'

# Bind alarming_queue to dlx for messages that expired from queue2 and rejected from queue1
rabbitmqadmin declare binding source=dlx destination=alarming_queue destination_type=queue \
  arguments='{"x-match":"all-with-x","x-death[queue1][rejected]-count":1,"x-death[queue2][expired]-count":1}'

# Publish a test message to queue1
rabbitmqadmin publish exchange="" routing_key=queue1 payload="test message"

1. Message is published to queue1
2. After the message is rejected, will be dead-lettered to the dlx exchange
3. The exchange maps the death info: x-death[queue1][rejected]-count = 1
4. Message routes to queue2 (matches the first binding)
5. After a second message expired from queue2
6. Now the exchange has the message with headers: x-death[queue1][rejected]-count = 1 AND x-death[queue2][expired]-count = 1
7. Message routed to alarming_queue (matches the second binding requiring both conditions), besides also being routed to queue2.

The exchange supports all standard headers exchange matching modes:

• all: All headers (excluding x-prefixed) must match
• any: Any header (excluding x-prefixed) must match
• all-with-x: All headers (including x-death mapped headers) must match
• any-with-x: Any header (including x-death mapped headers) must match

For x-death routing capabilities that this exchange provides, you'll need to use all-with-x or any-with-x modes.

This project is licensed under the Mozilla Public License 2.0 - see the LICENSE file for details.