Lambda continues to run after ApiGateway request timed out

Question

I set up an API Gateway endpoint, Lambda integration, default timeout (29s).  
  
The Lambda sleeps for 40 seconds, then logs.  
  
We observe the following:  
- 29 seconds after issuing the request, we receive `{"message": "Endpoint request timed out"}`  
- 40 seconds in, the Lambda logs  
  
Why does the Lambda continue to run AFTER the request timed out? Currently, we rely on this behaviour - is it safe to assume things will stay this way, or could this change?  
  
Edited by: mjfroehlich on Apr 26, 2019 5:32 AM

Answer

Timeout happens in the API Gateway side, so Lambda will continue to execute your function. This is true for most HTTP client-server scenario. The client-side timeout does not guarantee to abort the execution in the server.  
  
If you don't need to wait/return Lambda's response via API Gateway, then why don't you invoke it asynchronously?  
https://docs.aws.amazon.com/apigateway/latest/developerguide/set-up-lambda-integration-async.html

Answer

Nice, thanks for the pointer!

Lambda continues to run after ApiGateway request timed out

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