Flash magazines before shutting down Lambda

Question

I am writing a NodeJS / Typescript registration service for AWS Lambda, and I noticed that there are four ways to complete the lambda function:

• Default. All callbacks are complete and Lambda will complete the execution.

• Error. There is an uncaught exception or an unhandled rejection, and it calls Lambda and calls process.exit().

• Time-out. Lambda runs more than the time specified by the developer.
• Managed termination. Lambda completes execution by calling context.done(), context.succeed()or context.fail(). This is no longer offered, should be used instead callback().

I want my logger to be able to clear all the logs no matter how Lambda completes, and this is what I used with various completion methods:

• Default. I wrapped the handler and the callback function to clear the logs before calling the callback function, and it worked perfectly.

  wrap(fn) {
      return () => {
          // Wrap the callback function
          let callbackFunc = arguments[arguments.length - 1];
          let wrappedCallback = this.wrapCallback(callbackFunc);
          arguments[arguments.length - 1] = wrappedCallback;
  
          return fn.apply(this, arguments);
      };
  }
  
  wrapCallback(fn) {
      return () => {
          logger.flush();
          return fn.apply(this, arguments);
      };
  

• Error. I added code to catch process.exit errors and it worked.

  process.on('unhandledRejection', (reason, p) => {
      logErrorAndFlusgLogs();
  }).on('uncaughtException', err => {
      logErrorAndFlusgLogs();
  }).on('exit', (code) => {
      logErrorAndFlusgLogs();
  });
  

But for “Timeout” and “Controlled completion”, none of the functions work above, and I could not find a way to catch it and clear the logs before Lambda completed, any idea on how to do this? Thank.

Answer 1

Timeouts are processed by a lambda container. There is currently no signal or callback, so in this case it is best to set the timer to expire a few minutes before the timeout value in order to clear the logs and stop the lambda yourself.

context.done, context.succeed context.fail:

const { done, succeed, fail } = context;

context.done = (...params) => {
    logErrorAndFlushLogs();
    done(...params);
};

context.succeed = (...params) => {
    logErrorAndFlushLogs();
    succeed(...params);
};

context.fail = (...params) => {
    logErrorAndFlushLogs();
    fail(...params);
};