Is it possible to keep an AWS Lambda function warm?

Question

There are a few pieces of my app that cannot afford the additional 1-2 second delay caused by the "freeze-thaw" cycle that Lambda functions go through when they're new or unused for some period of time.

How can I keep these Lambda functions warm so AWS doesn't have to re-provision them all the time? This goes for both 1) infrequently-used functions and 2) recently-deployed functions.

Ideally, there is a setting that I missed called "keep warm" that increases the cost of the Lambda functions, but always keeps a function warm and ready to respond, but I'm pretty sure this does not exist.

I suppose an option is to use a CloudWatch timer to ping the functions every so often... but this feels wrong to me. Also, I don't know the interval that AWS uses to put Lambda functions on ice.

Answer 1

BBC has published a nice article on iPlayer engineering where they describe a similar issue.

They have chosen to call the function every few minutes using CloudWatch Scheduled Events.

So in theory, it should just stay there, except it might not. So we have set up a scheduled event to keep the container ‘warm’. We invoke the function every couple of minutes not to do any processing, but to make sure we’ve got the model ready. This accounts for a very small percentage of invocations but helps us mitigate race conditions in the model download.(We also limit artificially how many lambdas we invoke in parallel as an additional measure).

Answer 2

UPDATE DEC 2019

AWS now also offers 'Provisioned Concurrency'. https://aws.amazon.com/blogs/aws/new-provisioned-concurrency-for-lambda-functions/

Basically you pay around 10$/month (for a 1GB Lambda) per instance that you want to keep 'warm'.