AWS Lambda (Node.js, v. 8.10) & Mongoose: MongoNetworkError connection to DB timed out

Question

Env.:

• AWS Lambda (Node.js, v. 8.10), waitForEmptyEventLoop === false
• MongoDB (Atlas)
• Mongoose

Problem: sometimes (randomly) I get next error:

MongoNetworkError: connection 6 to db_host:27017 timed out
  File "/opt/nodejs/node_modules/mongodb-core/lib/connection/connection.js", line 259, col 7, in TLSSocket.<anonymous>
    new MongoNetworkError(f('connection %s to %s:%s timed out', self.id, self.host, self.port)),
  File "events.js", line 313, col 30, in Object.onceWrapper
  File "events.js", line 106, col 13, in emitNone
  File "events.js", line 208, col 7, in TLSSocket.emit
  File "net.js", line 420, col 8, in TLSSocket.Socket._onTimeout
  File "timers.js", line 482, col 11, in ontimeout
  File "timers.js", line 317, col 5, in tryOnTimeout
  File "timers.js", line 277, col 5, in Timer.listOnTimeout

Code of db connection:

const mongoose = require('mongoose');
const log = require('./log');

const options = {
  reconnectTries: 30,
  reconnectInterval: 500,
  poolSize: Number(process.env.DB_POOLSIZE) || 1,
  socketTimeoutMS: 30000,
  keepAlive: true,
  bufferCommands: false,
  bufferMaxEntries: 0,
};

let isConnected;

module.exports.connect = () => new Promise((resolve, reject) => {
  if (isConnected) {
    return resolve();
  }

  return mongoose.connect(process.env.DB_URI, options)
    .then((db) => {
      isConnected = db.connections[0].readyState;
      resolve();
    }).catch((error) => {
      log.error('DB:', error);
      reject(error);
    });
});

I've checked - isConnected cached successfully, mongodb connection cached in mongoose. All must be okay, but sometimes I get this error.

Anybody have any ideas how can I solve this issue?

Answer 1

Just increase socketTimeoutMS - for me 2000000 enough to keep connection between lambdas invocation of "warm" container. Use next config (mongoose):

 { reconnectTries: 30, reconnectInterval: 500, poolSize: 1, socketTimeoutMS: 2000000, keepAlive: true, }

Another variant (smbd treat this as best practice) - create/close connection for each lambda invocation. Not bad idea if you know that lambda will invoked rarely