CODEWITHSUNDEEP
aws-lambda
tschumann
tschumann

Reputation: 3246

handle shutdown of Java AWS Lambda

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.

Upvotes: 9

Views: 5443

Answers (4)

Comencau
Comencau

Reputation: 1193

It seems it is now possible with Lambda Extensions : https://docs.aws.amazon.com/lambda/latest/dg/runtimes-extensions-api.html.

If an extension is registered, then Lambda will send a SIGTERM and let 300 ms for your code to react and make the clean up you need (closing the connections in your database connections pool).

See : https://github.com/aws-samples/graceful-shutdown-with-aws-lambda

Upvotes: 2

Brett Ryan
Brett Ryan

Reputation: 28255

Assuming you have a pooled connection for a warm lambda, you may register a shutdown hook to close the DB connection or release any other resources, you only have 500 ms to perform this task.

class EnvironmentConfig {

    private static volatile boolean shutdownRegistered;
    private static volatile HikariDataSource ds;

    private void registerShudownHook() {
        if (!shutdownRegistered) {
            synchronized (lock) {
                if (!shutdownRegistered) {
                    Runtime.getRuntime().addShutdownHook(new Thread(() -> {
                        if (ds != null) {
                            ds.close();
                        }
                    }));
                    EnvironmentConfig.shutdownRegistered = true;
                }
            }
        }
    }

    public DataSource dataSource() throws PropertyVetoException {
        HikariDataSource _ds = EnvironmentConfig.ds;
        if (_ds == null) {
            synchronized (lock) {
                _ds = EnvironmentConfig.ds;
                if (_ds == null) {
                    _ds = new HikariDataSource();
                    // TODO: set connection props
                    EnvironmentConfig.ds = _ds;
                    registerShudownHook();
                }
            }
        }
        return _ds;
    }

}

You can reference the datasource anywhere to get a singleton copy which will create the instance and register the shutdown hook.

Your shutdown hook could do other tasks, provided it does them quickly, or you can register more than one hook, just don't go nuts with how many threads you're registering.

Upvotes: 2

s.hesse
s.hesse

Reputation: 2060

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.

Upvotes: 3

Maurice
Maurice

Reputation: 13118

No, you can't hook into the shutdown of a Lambda Execution context.

Lambda handles that on it's own an decides if and when to re-use or destroy execution contexts.

You'll probably have to rely on the connections to time out on their own.

Upvotes: 0

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