Watchdog timeout utility for aws serverless applications.

watchdog.js

export function watchDog(event, context) {
  let messageStack = [];
  let timeoutId;

  const push = function(message) {
    messageStack.push(message);
  };

  const setupTimer = function(event, context, callback) {
    messageStack.push('Start');

    const timeoutHandler = () => {
      console.error(
        'WatchDog timed out: ',
        readable(messageStack),
        readable(event),
        readable(context)
      );

      if (typeof callback === 'function') {
        callback();
      }
    };

    timeoutId = setTimeout(timeoutHandler, context.getRemainingTimeInMillis() - 1000);
  };

  const end = function() {
    clearTimeout(timeoutId);
  };

  setupTimer(event, context);

  return Object.freeze({
    push: push,
    end: end,
  });
}

function readable(obj) {
  if (typeof obj === 'string') {
    return obj;
  }

  try {
    return JSON.stringify(obj, null, 2);
  } catch (err) {
    return String(obj);
  }
}

Example usage inside a lambda handler.

export const handler = function(event, context) {
  const WatchDog = new watchDog(event, context);

  WatchDog.push('Example');

  WatchDog.end();

  return {};
}