# RabbitMQ based

* [rabbitmq\_delayed\_message\_exchange plugin](#rabbitmq_delayed_message_exchange-plugin)
  * [Flowchart](#flowchart)
  * [Cons](#cons)
* [Dead letter queue](#dead-letter-queue)
  * [Flowchart](#flowchart-1)
  * [Cons](#cons-1)

## rabbitmq\_delayed\_message\_exchange plugin

### Flowchart

1. The message will be put into delayed exchange. Within delayed exchange, the message will be stored inside Mnesia (A file-based database).
2. Once the delayed period is passed, messages will be delivered to the message queue.

![](https://1010073591-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-Mk8dv8Mfudl_6ziUzDf%2Fuploads%2Fgit-blob-0c867c9ae5482dddd93d73c86375229515b2e2cd%2FdelayQueue_rabbitmq_plugin.png?alt=media)

### Cons

* Before messages are delivered to target queue, they are stored in servers' local file-based DB Mnesia. If the node becomes unavailable or the data has not been flushed to disk, they will be lost.
* It does not support high concurrent volume and big data size.

## Dead letter queue

### Flowchart

1. Delay queue has no consumers and an expiration time.
2. When messages get expired, they will be delivered to dead letter queue.

![](https://1010073591-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-Mk8dv8Mfudl_6ziUzDf%2Fuploads%2Fgit-blob-4a113c9843bb269fbe0df0d231cbf7b269a8b553%2FdelayQueue_dlq.png?alt=media)

### Cons

* TTL threshold is set on the queue level. Each queue will have a different expiration time. If customized delay time is needed, then lots of queue need to be created.