AWS Lambda Functions: Will Different Triggers Reuse an Exection Enviornment?

Question

Here's what I know, or think I know.

In AWS Lambda, the first time you call a function is commonly called a "cold start" -- this is akin to starting up your program for the first time.

If you make a second function invocation relatively quickly after your first, this cold start won't happen again. This is colloquially known as a "warm start"

If a function is idle for long enough, the execution environment goes away, and the next request will need to cold start again.

It's also possible to have a single AWS Lambda function with multiple triggers. Here's an example of a single function that's handling both API Gateway requests and SQS messages.

My question: Will AWS Lambda reuse (warm start) an execution environment when different event triggers come in? Or will each event trigger have it's own cold start? Or is this behavior that's not guaranteed by Lambda?

Answer 1

Yes, different triggers will use the same containers since the execution environment is the same for different triggers, the only difference is the event that is passed to your Lambda.

You can verify this by executing your Lambda with two types of triggers (i.e. API Gateway and simply the Test function on the Lambda Console) and looking at the CloudWatch logs. Each Lambda container creates its own Log Stream inside of your Lambda's Log Group. You should see both event logs going to the same Log Stream which means the 2nd event is successfully using the warm container created by the first event.