# Fan Out Pattern

## Basics

* When a message needs to be send to multiple SQS queues, this pattern is useful.
* A message is first pushed to an SNS topic and SQS queues are subscribers to these topics.
* Due to this fan out pattern,
  * One can easily add new queues as subscriber
  * Application architecture becomes fully decoupled as there is no data loss.
  * Allows for data persistence, delayed processing and introduce retries.
* Make sure your SQS queue access policy allows for SNS to write.
* Cross-Region Delivery: SNS Topics in one region can send message to SQS queues in other region/s provided access has been given.

## Diagram

![SQS-SNS\_Fanout](/files/RR3BrqPEjcXKdqtmYotq)

## Applications

### S3 and Fanout Pattern

* One of the application of this pattern is for combination of event type and prefix, you can use only one S3 Event Rule.
* If you want to send the same S3 event to many SQS queues, use Fan-Out pattern.

![S3 And Fanout Integration](/files/TGu2mDM4UfJOFLz7g4oJ)

### SNS -> Kinesis Data Firehose -> S3 Kinesis

* SNS can be directly integrated to Kinesis Data Firehose.
* This integration can be leveraged to send data to S3.

![SNS and S3 Integrations](/files/7KfnESYRfzMtGkyAHRKo)


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