SequelizeConnectionError in Node.js application

Question

I have strange problem and don't know in what place is the problem. I will be grateful for any help.

I have Node.js application which works fine in local windows 10 computer. I run this application successfully in Docker which is in CentOS server. This application works with remote MySQL and PostgreSQL databases. It worked correctly several days but yestoday I notice that I have error. Application can't connect to remote MySQL database anymore. In the same time I can connect to that remote MySQL database without any problem if I run application in my local computer or connect by DBeaver/dbForge tool.

MySQL.js:

const Sequelize = require('sequelize');

const sequelize = new Sequelize('database_name', 'username', 'password', {
    host: 'host',
    dialect: 'mysql'
});

sequelize.authenticate().then(() => {
    console.log('Connection to database has been established successfully.');
}).catch(err => {
    console.error('Unable to connect to database:', err);
});

module.exports = sequelize;

routes.js:

const express = require('express');

const router = express.Router();

const sequelize = require('../configurations/MySQL');
const Sequelize = require('sequelize');

const passport = require('passport');
require('../configurations/password')(passport);

router.post('/search_by_name', passport.authenticate('jwt', {session: false}, null), function(req, res) {
    const token = getToken(req.headers);
    if (token) {
        sequelize.query("LONG SQL QUERY", {
            replacements: {
                name: req.body.name,
            },
            type: Sequelize.QueryTypes.SELECT
        }).then((locations) => {
            res.status(200).send(locations)
        }).catch((error) => {
            res.status(400).send(error);
        });
    } else {
        return res.status(401).send({
            status: false,
            description: "Unauthorized"
        });
    }
});

As you can see I use sequelize library to connect application to remote MySQL database. The same library I use to connect to remote PostgreSQL database. As I said before error happens only when I try to connect to remote MySQL database in Docker. There is no error with PostgreSQL connection in Docker. Is it possible that problem inside Docker/network?

Dependencies:

"sequelize": "^4.42.0"
"mysql2": "^1.6.4"

I also thought that the reason of the problem can be because of much pools/connections and sequelize library don't close them automatically. For thats why I restarted docker сontainer several times hoping to confirm the theory. Unfortunately the error do not disappear.

How do you think, what happens?

Error:

Unable to connect to the database: { SequelizeConnectionError: connect ETIMEDOUT
    at Utils.Promise.tap.then.catch.err (/node_modules/sequelize/lib/dialects/mysql/connection-manager.js:149:19)
    at tryCatcher (/node_modules/bluebird/js/release/util.js:16:23)
    at Promise._settlePromiseFromHandler (/node_modules/bluebird/js/release/promise.js:512:31)
    at Promise._settlePromise (/node_modules/bluebird/js/release/promise.js:569:18)
    at Promise._settlePromise0 (/node_modules/bluebird/js/release/promise.js:614:10)
    at Promise._settlePromises (/node_modules/bluebird/js/release/promise.js:690:18)
    at _drainQueueStep (/node_modules/bluebird/js/release/async.js:138:12)
    at _drainQueue (/node_modules/bluebird/js/release/async.js:131:9)
    at Async._drainQueues (/node_modules/bluebird/js/release/async.js:147:5)
    at Immediate.Async.drainQueues [as _onImmediate] (/node_modules/bluebird/js/release/async.js:17:14)
    at processImmediate (timers.js:632:19)
  name: 'SequelizeConnectionError',
  parent:
   { Error: connect ETIMEDOUT
       at Connection._handleTimeoutError (/node_modules/mysql2/lib/connection.js:173:17)
       at listOnTimeout (timers.js:324:15)
       at processTimers (timers.js:268:5)
     errorno: 'ETIMEDOUT',
     code: 'ETIMEDOUT',
     syscall: 'connect',
     fatal: true },
  original:
   { Error: connect ETIMEDOUT
       at Connection._handleTimeoutError (/node_modules/mysql2/lib/connection.js:173:17)
       at listOnTimeout (timers.js:324:15)
       at processTimers (timers.js:268:5)
     errorno: 'ETIMEDOUT',
     code: 'ETIMEDOUT',
     syscall: 'connect',
     fatal: true }}

Answer 1

Try to add pool option when new Sequelize. Reference document

Sequelize will setup a connection pool on initialization so you should ideally only ever create one instance per database if you're connecting to the DB from a single process. If you're connecting to the DB from multiple processes, you'll have to create one instance per process, but each instance should have a maximum connection pool size of "max connection pool size divided by number of instances". So, if you wanted a max connection pool size of 90 and you had 3 worker processes, each process's instance should have a max connection pool size of 30.

const Sequelize = require('sequelize');

const sequelize = new Sequelize('database_name', 'username', 'password', {
    host: 'host',
    dialect: 'mysql',
    pool: {
      max: 15,
      min: 5,
      idle: 20000,
      evict: 15000,
      acquire: 30000
    },
});

module.exports = sequelize;

Also, you can check more option at here

options.pool sequelize connection pool configuration

options.pool.max default: 5 Maximum number of connection in pool

options.pool.min default: 0 Minimum number of connection in pool

options.pool.idle default: 10000 The maximum time, in milliseconds, that a connection can be idle before being released. Use with combination of evict for proper working, for more details read https://github.com/coopernurse/node-pool/issues/178#issuecomment-327110870

options.pool.acquire default: 10000 The maximum time, in milliseconds, that pool will try to get connection before throwing error

options.pool.evict default: 10000 The time interval, in milliseconds, for evicting stale connections. Set it to 0 to disable this feature.

options.pool.handleDisconnects default: true Controls if pool should handle connection disconnect automatically without throwing errors

options.pool.validate A function that validates a connection. Called with client. The default function checks that client is an object, and that its state is not disconnected