Exchanges

Exchanges receive published messages and route them to queues based on bindings and routing rules. Each exchange type implements a different routing strategy.

Common Properties

Property	Description
name	Exchange name. The default exchange has an empty name.
type	Routing algorithm (direct, fanout, topic, headers, x-consistent-hash, x-delayed-message)
durable	Survives server restart
auto_delete	Deleted when the last binding is removed
internal	Cannot be published to directly by clients
arguments	Optional arguments (alternate exchange, deduplication, delayed, etc.)

Exchange Types

Direct Exchange

Routes messages to queues where the binding key exactly matches the routing key.

• Pre-declared: amq.direct
• One message can be delivered to multiple queues if they share the same binding key

Fanout Exchange

Routes messages to all bound queues, ignoring the routing key.

• Pre-declared: amq.fanout
• Most efficient for broadcast patterns

Topic Exchange

Routes messages by pattern matching on the routing key. The routing key is a dot-separated string (e.g., stock.nyse.ibm).

• Pre-declared: amq.topic
• * (star) matches exactly one word
• # (hash) matches zero or more words

Examples:

• Binding stock.*.ibm matches stock.nyse.ibm but not stock.nyse.sub.ibm
• Binding stock.# matches stock.nyse.ibm, stock, and stock.nyse
• Binding # matches everything (acts as fanout)

Headers Exchange

Routes based on message header matching rather than the routing key.

• Pre-declared: amq.headers, amq.match
• Binding arguments specify the headers to match
• x-match argument controls matching behavior:
  • all (default) — all specified headers must match
  • any — at least one header must match
• Headers starting with x- are ignored during matching

Consistent Hash Exchange

Distributes messages across bound queues using consistent hashing. Each message is routed to exactly one queue.

• Type: x-consistent-hash
• The binding key must be a number representing the queue's weight
• Higher weight means a larger share of messages
• x-hash-on exchange argument selects what to hash on (default: routing key). Set it to a header name to hash on a header value instead.
• x-algorithm exchange argument selects the hash algorithm: ring or jump. The server-wide default is configurable:

Config Key	Section	Default	Description
default_consistent_hash_algorithm	[main]	ring	Default hash algorithm when x-algorithm is not set on the exchange

Default Exchange

A nameless direct exchange that every queue is automatically bound to, with the queue's name as the binding key. Publishing to the default exchange with a routing key equal to a queue name delivers directly to that queue.

Cannot be deleted, and cannot be explicitly bound to.

• Pre-declared: amq.default (display name only)

Alternate Exchanges

An alternate exchange receives messages that would otherwise be unroutable (no matching bindings on the primary exchange).

Set via the x-alternate-exchange argument (or alternate-exchange) when declaring the exchange, or via the alternate-exchange policy.

If the alternate exchange also cannot route the message, the message is discarded (or returned to the publisher if the mandatory flag was set on the publish).

Delayed Exchanges

Any exchange can be made into a delayed exchange. See Delayed Queues for details.

Declare the exchange with type x-delayed-message and the underlying type as the x-delayed-type argument. Alternatively, apply the delayed-message policy to an existing exchange. Messages with an x-delay header are held in an internal queue and delivered after the delay expires.

Log Exchange

When enabled, LavinMQ declares an internal topic exchange named amq.lavinmq.log and publishes server log records to it. The routing key is the log severity (e.g., Info, Warn, Error) and the body contains the log source and message.

Config Key	Section	Default	Description
log_exchange	[main]	false	Publish server log records to amq.lavinmq.log

Exchange-to-Exchange Bindings

Exchanges can be bound to other exchanges. When a message matches a binding, it is forwarded to the destination exchange, which then routes it using its own bindings. This allows building routing topologies.