handle shutdown of Java AWS Lambda

Question

Is there a way to hook into a Lambda's shutdown? I am opening a database connection and want to keep it open, but I want to make sure it gets closed when the Lambda is terminated.

Answer 1

You are probably interested in an event that is thrown when the Lambda instance is being killed and not when a single invocation ends, right? You have one option for both though, but I doubt that they'll help you..

You can either use the context method getRemainingTimeInMillis() (links to Node.js but similar in other programming languages) to find out when the current invocation of your Lambda function times out. This might be helpful to cleanup things or use the time of your Lambda function to the full extent. I don't recommend to cleanup your database connections at the end of each invocation because then you won't reuse them for future invocations which slows down your Lambda function. But if you're okay with that, then go for it. Remember that this only works as long as your function is running. As soon as you have returned a response, you can't perform any cleanup operations because your Lambda function will get into a 'sleep mode'. You need to do this before you return something.

Alternatively, you can make use of the Extensions API. It offers a shutdown phase and triggers an extension with a Shutdown event. However, since an extension sits besides your function (and not within your function code), I'm not sure if you have a chance to clean up any database connections with this approach... See also Lambda Execution Environment for additional information.