DB Connection Unavailable Lambda with Cloud Watch Event Rules - amazon-web-services

Question

I'm having issues connecting to mongodb when I am using a cloud watch event rule to trigger lambdas to keep them warm and also the same issue when I tried using serverless-plugin-warmup. Anyone have and ideas as to why this would be happening? Also I whitelist IP's for my database and use an Elastic IP for my lambda functions. Could the cloud watch event rules be causing the lambdas to use a different IP?
{"error":{"name":"MongoError","message":"no connection available"}}
I wrap my functions with the following to make sure the database is connected before running code
const mongoose = require('mongoose');
mongoose.Promise = global.Promise;
let cachedDB = null;
module.exports = fn => (...args) => {
const [, context] = args;
context.callbackWaitsForEmptyEventLoop = false;
if (cachedDB && cachedDB.readyState != 0 && cachedDB.readyState != 3) {
fn(...args);
} else {
mongoose.connect(process.env.MONGO_URI);
mongoose.connection.on('error', err => {
console.log('Connection Error');
console.log(err);
});
mongoose.connection.once('open', () => {
cachedDB = mongoose.connection;
fn(...args);
});
}
};

Answer 1

You need to handle warmup events as a special case in your handler. Basically, your handler should return right away when it is invoked via a warmup event.
In the example given in serverless-warmup-plugin, you can do it this way,
module.exports.lambdaToWarm = function(event, context, callback) {
// Immediate response for WarmUP plugin
if (event.source === 'serverless-plugin-warmup') {
console.log('WarmUP - Lambda is warm!')
return callback(null, 'Lambda is warm!')
}
// add lambda logic after
}
Notice that there is an if statement at the beginning to check if it's a warmup event. If it is, return successfully right away.
This check should be at the beginning so that it doesn't have to connect to MongoDB at all.