This document summarizes RabbitMQ, an open source message broker. It discusses the key components - producers, exchanges, bindings, queues, and consumers. Producers publish messages to exchanges. Exchanges route messages to queues based on routing keys and exchange type (direct, topic, fanout). Consumers consume messages from queues. It also covers topics like dead letter exchanges, acknowledgements, and remote procedure calls.

1. RabbitMQ
message broker

2. How it works

3. Producer
• Also known as Publisher
• Part of user application
• Publishes messages to exchange (with routing key)

4. Exchange
• Exchanges messages between producer and queues
• Queue(s) selection depends on
• Exchange type
• Queue bindings
• Routing key the message is published with

5. Exchange types
• Direct - match exact routing keys
• Topic - match pattern routing keys
• Fanout - match all routing keys (ignores them)
• Headers - match exact message headers (all or any)

6. Bindings
• Also known as Routes
• Connection between exchange and queue/exchange
• Exchange can be bound to multiple queues
• Queue can be bound to multiple exchanges
• Exchange/Queue can be bound by multiple bindings

7. Direct routing

8. Direct routing
• Example: ImageProcessorExchange
• Image file path is sent in message body
• ImageWatermarkQueue - `image.watermark`
• Stores paths of images to watermark
• Consumer applies watermark to images
• ImageResizeQueue - `image.resize`
• Stores paths of images to watermark
• Consumer resizes images

9. Topic routing

10. Topic routing
• Example: LoggerExchange <channel>.<log level>
• FileLoggerQueue - `#`
• Stores all message
• Consumer logs message to file
• SmsLoggerQueue - `*.critical`, `*.emergency`
• Stores all critical and emergency messages
• Consumer sends alert SMS to IT support phone

11. Fanout routing

12. Fanout routing
• Example: OrderCreatedExchange
• OrderCreatedSMSQueue
• Consumer sends SMS message to customer
• OrderCreatedMailQueue
• Consumer sends mail to customer
• OrderCreatedExportQueue
• Consumer exports order to ERP system

13. Headers routing
• Example: FileUploadExchange
• Message with `format` header and file content in body
• ImageUploadQueue - `format=jpeg`, `format=png`
• Stores jpeg and png image files
• Consumer resizes, applies watermark and saves image
• VideoUploadQueue - `format=mp4`, `format=avi`
• Stores mp4 and avi video files
• Consumer resamples video to multiple resolutions
• Another VideoResampleExchange can be used to faster resampling

14. Queue
• FIFO - first in first out
• Stores messages until consumed by consumer
• Every queue is bind to default exchange
• Queue name is used as routing key
• Can be used for Dead Letter Exchange or RPC

15. Consumer
• Part of user application
• Consumes messages from queue
• Needs to acknowledge message
• Only if the message’s delivery mode is persistent
• Multiple instances can be used for faster processing

16. Message acknowledgement
• Acknowledge
• Reject
• Drop
• Re-queue (infinite loops may occur)
• Use Dead Letter Exchange instead

17. Questions?
we are not finished yet

18. Dead Letter Exchange
DLX

19. Dead Letter Exchange
• Allows safe rejecting messages
• not using re-queue (infinite loops)
• moves them to another queue
• Move messages back after you fix issue causing reject
• Messages can be moved back automatically after delay

20. Dead Letter Exchange
• While declaring queue `queue.one` use arguments
• x-dead-letter-exchange: `` //default exchange
• x-dead-letter-routing-key: `queue.one.dlx`
• Declare additional queue `queue.one.dlx`
• Now every time message from `queue.one` is rejected
(without re-queue) it is automatically dead lettered to
`queue.one.dlx`.

21. Dead Letter Exchange
• To automatically move messages back to original queue
you need to declare `queue.one.dlx` with dead letter
arguments routing back to original queue
• Now when `queue.one.dlx` message is rejected it will be
moved back to queue `queue.one`
• To automatically reject message after delay declare queue
`queue.one.dlx` with argument `x-message-ttl`. As value
use timeout in milliseconds

22. Remote Procedure
Call
RPC

23. Remote Procedure Call
• Sometimes you need to wait for response
• Useful for multiple (time consuming) calculations at same
time
• 10s and 15s calculations will last 15s instead of 25s

24. Remote Procedure Call
• RPC client (Publisher)
• generates temporary queue
• publishes message to RPC server’s exchange
• with generated queue name in message header
• starts consuming generated queue (timeout is
recommended)

25. Remote Procedure Call
• RPC server (Consumer)
• processes message from RPC client
• publishes response to default exchange
• using generated queue name from message header
as routing key

26. Questions?

27. Thanks!
Vít Kutný
https://vitkutny.cz