# REL05-BP02 Throttle requests
<a name="rel_mitigate_interaction_failure_throttle_requests"></a>

 Throttling requests is a mitigation pattern to respond to an unexpected increase in demand. Some requests are honored but those over a defined limit are rejected and return a message indicating they have been throttled. The expectation on clients is that they will back off and abandon the request or try again at a slower rate. 

 Your services should be designed to handle a known capacity of requests that each node or cell can process. This capacity can be established through load testing. You then need to track the arrival rate of requests and if the temporary arrival rate exceeds this limit, the appropriate response is to signal that the request has been throttled. This allows the user to retry, potentially to a different node or cell that might have available capacity. Amazon API Gateway provides methods for throttling requests. Amazon SQS and Amazon Kinesis can buffer requests, smooth out the request rate, and alleviate the need for throttling for requests that can be addressed asynchronously. 

 **Level of risk exposed if this best practice is not established:** High 

## Implementation guidance
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+  Throttle requests. This is a mitigation pattern to respond to an unexpected increase in demand. Some requests are honored but those over a defined limit are rejected and return a message indicating they have been throttled. The expectation on clients is that they will back off and abandon the request or try again at a slower rate. 
  +  Use Amazon API Gateway 
    +  [Throttle API Requests for Better Throughput](https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-request-throttling.html) 

## Resources
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 **Related documents:** 
+  [Amazon API Gateway: Throttle API Requests for Better Throughput](https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-request-throttling.html) 
+  [Error Retries and Exponential Backoff in AWS](https://docs.aws.amazon.com/general/latest/gr/api-retries.html) 
+  [The Amazon Builders' Library: Avoiding fallback in distributed systems](https://aws.amazon.com/builders-library/avoiding-fallback-in-distributed-systems) 
+  [The Amazon Builders' Library: Avoiding insurmountable queue backlogs](https://aws.amazon.com/builders-library/avoiding-insurmountable-queue-backlogs) 
+  [The Amazon Builders' Library: Timeouts, retries, and backoff with jitter](https://aws.amazon.com/builders-library/timeouts-retries-and-backoff-with-jitter/) 
+  [Throttle API Requests for Better Throughput](https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-request-throttling.html) 

 **Related videos:** 
+  [Retry, backoff, and jitter: AWS re:Invent 2019: Introducing The Amazon Builders’ Library (DOP328)](https://youtu.be/sKRdemSirDM?t=1884)