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Similar to RabbitMQ - message broker
RabbitMQ - message broker
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- 3. Producer • Also knownas Publisher • Part of user application • Publishes messages to exchange (with routing key)
- 4. Exchange • Exchanges messagesbetween 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 knownas 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
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- 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
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- 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
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- 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 ofuser 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 notfinished yet
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- 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
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- 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
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