How to optimize AWS Lambda?

Question

I'm currently building web API using AWS Lambda with Serverless Framework.

In my lambda functions, each of them connects to Redis (elasticache) and RDB (Aurora, RDS) or DynamoDB to retrieve data or write new data. And all my lambda functions are running in my VPC.

Everything works fine except that when a lambda function is first executed or executed a while after last execution, it takes quite a long time (1-3 seconds) to execute the lambda function, or sometimes it even respond with a gateway timeout error (around 30 seconds), even though my lambda functions are configured to 60 seconds timeout.

As stated in here, I assume 1-3 seconds is for initializing a new container. However, I wonder if there is a way to reduce this time, because 1-3 seconds or gateway timeout is not really an ideal for production use.

If you don't want the Cold Start delay, you may try to keep ping your API once every minutes to prevent the instance go to sleep due to idle. Setting a higher RAM will also speed up the cold start as this affect the CPU allocation too. But for the 30s timeout, its definitely something wrong. — Nick

Seafish Seafish · Accepted Answer · 2016-06-06T22:42:31

You've go two issues:

The 1-3 second delay. This is expected and well-documented when using Lambda. As @Nick mentioned in the comments, the only way to prevent your container from going to sleep is using it. You can use Lambda Scheduled Events to execute your function as often as every minute using a rate expression rate(1 minute). If you add some parameters to your function to help you distinguish between a real request and one of these ping requests you can immediately return on the ping requests and then you've worked around your problem. It will cost you more, but we're probably talking pennies per month if anything. Lambda has a generous free tier.
The 30 second delay is unusual. I would definitely check your CloudWatch logs. If you see logs from when your function is working normally but no logs from when you see the 30 second timeout then I would assume the problem is with API Gateway and not with Lambda. If you do see logs then maybe they can help you troubleshoot. Another place to check is the AWS Status Page. I've seen sometimes where Lambda functions timeout and respond intermittently and I pull my hair out only to realize that there's a problem on Amazon's end and they're working on it.

Here's a blog post with additional information on Lambda Container Reuse that, while a little old, still has some good information.

How to optimize AWS Lambda?

1 Answers