The short answer: Lambda@Edge is limited to a 5 seconds timeout
The reason: If you configured your lambda to a larger timeout (let's say 58 sec), when you deploy it to Lambda@edge, AWS would automatically adjust the number to a lower number (for us it was 1 second).
The solution is simple: You should not configure your Lambda functions that will be deployed to Lambda@Edge for more than 5 seconds.
How Trace it?
1. You get a 503 when you try to login a Cognito secured site for example with "The Lambda function associated with the CloudFront distribution is invalid or doesn't have the required permissions"
2. When you go to the CloudWatch to examine the logs, you find out, that some function end after 1000 ms.
Keep Performing,
Moshe Kaplan
