Async Lambda retries conflicting documentation

Question

Hello,  
  
Getting up to speed on Lambda limits and reading through the docs and faqs I have found conflicting retry behaviour for asynchronous invocation:  
  
"Lambda functions being invoked asynchronously are retried at least 3 times."  
source: https://aws.amazon.com/lambda/faqs/  
  
"Asynchronous invocation: If your Lambda function is invoked asynchronously and is throttled, AWS Lambda automatically retries the throttled event for up to six hours, with delays between retries."  
source: https://docs.aws.amazon.com/lambda/latest/dg/concurrent-executions.html  
  
"If AWS Lambda is unable to fully process the event, it will automatically retry the invocation twice, with delays between retries"  
source: https://docs.aws.amazon.com/lambda/latest/dg/retries-on-errors.html  
  
I understand some of the docs may be specific to throttling and the retry policy for it may be different but it's unclear what's what.  
  
Does anyone know which one is right? I was mostly interested in throttling retry behaviour (max concurrency limit reached)  
  
Thanks

Accepted Answer

Hi Robert,  
  
All three documents you provided are correct though somewhat confusing. We categorize Lambda processing errors into system errors such as throttling and customer errors such as invalid runtime. System errors are retried for six hours with delays between retries; customer errors are retried twice. Hope this clarifies.  
  
Thanks  
Jia

Async Lambda retries conflicting documentation

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