Configure AWS Lambda handlers to keep them warm with Serverless and RDS.md

To use AWS Lambda (Serverless) with RDS in production, you should

• warm up functions
• preserve DRS connections

configure_handlers.js configures Serverless handler functions to achieve them.

Usage

const configure_handlers = require('./configure_handlers');

function create_user(event, context, handler_callback) {
  // Write you function
}

function list_users(event, context, handler_callback) {
  // Write you function
}

module.exports = configure_handlers({
  create_user,
  list_users,
});

References

• Keeping Functions Warm - How To Fix AWS Lambda Cold Start Issues
• How To: Reuse Database Connections in AWS Lambda

configure_handlers.js

'use strict';

function configure_handler(handler) {
  return (event, context, handler_callback) => {
    // ref: https://www.jeremydaly.com/reuse-database-connections-aws-lambda/
    context.callbackWaitsForEmptyEventLoop = false;

    // ref: https://github.com/FidelLimited/serverless-plugin-warmup
    if (event.source === 'serverless-plugin-warmup') {
      // TODO: Modify the response in accordance with your needs
      return handler_callback(null, { statusCode: 204 });
    }

    return handler(event, context, handler_callback);
  };
}

function configure_handlers(handlers) {
  const configured_handlers = {};

  Object.keys(handlers).forEach((handler_name) => {
    configured_handlers[handler_name] = configure_handler(handlers[handler_name]);
  });

  return configured_handlers;
}

module.exports = configure_handlers;