AMQP Message Flow Workbench

Trace one AMQP message from publisher to exchange, queue, consumer acknowledgment, requeue, dead letter, or mandatory return.

Interactive AMQP message flow animation showing channel setup, basic.publish, exchange routing, queue storage, publisher confirms, manual and automatic acknowledgements, prefetch, consumer crash redelivery, requeue, dead lettering, and mandatory returns.

AMQP Flow Reliability Acknowledgements

AMQP Message Flow Workbench

Send one message through an AMQP broker and watch the separate reliability loops: publisher confirm protects the publisher-to-broker handoff, while consumer acknowledgements control what happens after delivery.

Phase Setup

Publisher result Waiting

Queue state Ready

Consumer result Not delivered

1

Publish to an exchange

The producer sends Basic.Publish to an exchange with a routing key. It never pushes directly into a consumer.

2

Route into a queue

The exchange checks bindings. If a route exists, the broker places a copy into the matched queue.

3

Confirm publisher safety

Publisher confirms tell the sender the broker accepted the message. They do not mean the consumer processed it.

4

Acknowledge delivery

Manual ACK removes the message. Reject, NACK, or a consumer crash can requeue or dead-letter it.

Flow Controls

Choose a scenario, then step through the broker, publisher, and consumer outcomes.

Scenario Manual ACK: processed successfully Auto ACK: fast but unsafe Reject and requeue Reject to dead letter queue Consumer crash before ACK Durable path with confirms Unroutable mandatory publish

Scenarios set the important flags and outcome. You can adjust the controls after selecting one.

Acknowledgement mode

Manual mode keeps the message unacked until the consumer sends an ACK, NACK, reject, or disconnects.

Delivery mode

Persistent messages still need a durable queue and confirms if the publisher needs a durable handoff.

Consumer prefetch 1 message 3 messages 10 messages

Prefetch limits how many unacknowledged deliveries the broker can send to this consumer.

Durable queueQueue definition can survive broker restart when declared durable. Publisher confirmsThe broker sends Basic.Ack or Basic.Nack to the publisher after accepting or failing the publish. mandatory flagUnroutable messages are returned to the publisher instead of silently disappearing.

Animation controls

Step moves one protocol phase at a time so the two acknowledgement loops stay visible.

Force consumer outcome

Manual ACK: processed successfully

The message is accepted by the broker, routed to a queue, delivered to a consumer, and removed only after the consumer ACKs it.

message: persistent consumer: manual ACK route: matched

1. SetupChannel and bindings exist.

2. PublishProducer sends Basic.Publish.

3. ExchangeBinding rules are checked.

4. QueueMatched queue stores a copy.

5. ConfirmPublisher gets broker feedback.

6. DeliverConsumer receives the message.

7. OutcomeACK, requeue, DLQ, or return.

1

Producer sends Basic.Publish enters the exchange through an open channel.

2

Exchange decides The binding matches, so the queue can receive one copy.

3

Queue holds The broker stores the message until delivery and acknowledgement.

4

Consumer responds Manual ACK removes the message only after processing.

5

Final state The message is either done, requeued, dead-lettered, or returned.

Normal delivery path Return or requeue path Failure or dead letter path

Current Decision

The channel and bindings are ready. Publish the message and follow which party confirms which part of the journey.

Ready1

Unacked0

DLQ0

Protocol Trace

1. Channel.Open and Queue.Bind complete.
2. Waiting for Basic.Publish.

AMQP Flow Quick Reference

Publisher Confirms

• Confirm mode is a publisher-to-broker safety loop.
• Basic.Ack means the broker accepted responsibility for the publish.
• It does not prove that any consumer processed the message.

Consumer ACKs

• Manual ACK keeps a delivered message unacked until the consumer responds.
• ACK removes it; reject or NACK can requeue or dead-letter it.
• A channel or connection close requeues unacked deliveries.

Durability

• Use a durable queue and a persistent message for restart survival.
• Publisher confirms let the sender know the broker accepted the durable handoff.
• Transient messages prioritize speed over restart safety.

Prefetch

• Prefetch limits concurrent unacknowledged deliveries.
• prefetch=1 keeps one in-flight message per consumer.
• Higher values improve throughput but increase retry burst size.

Dead Lettering

• Reject or NACK with requeue=false can route to a DLX.
• TTL expiry, queue length limits, and delivery limits can also dead-letter.
• DLQs are for evidence, retry policy, and operator triage.

Common Confusion

• Publisher confirm and consumer ACK are separate guarantees.
• Auto ACK removes broker-side recovery after delivery.
• Mandatory return handles no-route publishes, not consumer failures.

Exchange Routing

Inspect direct, topic, fanout, and headers binding decisions.

Dead Letter Exchange

Follow failed messages into a DLX and DLQ with x-death evidence.

AMQP Frames

Review frame structure and channel multiplexing.

Virtual Hosts

See how broker namespaces isolate applications and permissions.