Connect Node.js to MongoDB, MySQL, PostgreSQL and Redis

Working connection code and settings for MongoDB, MySQL, PostgreSQL and Redis on DignityHost MERN hosting, plus pooling tips and common errors.

• Applies toMERN hosting plans
• Time needed20 min
• LevelIntermediate

Your application runs on the same server as the databases, so it connects to 127.0.0.1 and never travels over the internet. Create the database first, keep the credentials in environment variables, and reuse one connection (or pool) for the life of the process.

The API talks to the databases over localhost.

Get the credentials

MongoDB with Mongoose

const mongoose = require('mongoose');

async function connect() {
  await mongoose.connect(process.env.MONGODB_URI, { serverSelectionTimeoutMS: 8000, maxPoolSize: 5 });
  console.log('MongoDB connected');
}
connect().catch((e) => { console.error('MongoDB error', e.message); process.exit(1); });

MONGODB_URI=mongodb://dbuser:[email protected]:27017/dbname?authSource=dbname

• authSource is normally the database the user was created in.
• Percent-encode special characters in the password (@ becomes %40, / becomes %2F).
• Using MongoDB Atlas? Use the mongodb+srv:// string and allow your server's IP address in Atlas's Network Access list.

MySQL / MariaDB with mysql2

const mysql = require('mysql2/promise');

const pool = mysql.createPool({
  host: '127.0.0.1',
  user: process.env.DB_USER,
  password: process.env.DB_PASSWORD,
  database: process.env.DB_NAME,
  waitForConnections: true,
  connectionLimit: 5,
});

const [rows] = await pool.query('SELECT NOW() AS now');

PostgreSQL with pg

const { Pool } = require('pg');

const pool = new Pool({
  connectionString: process.env.DATABASE_URL, // postgresql://user:[email protected]:5432/dbname
  max: 5,
  idleTimeoutMillis: 30000,
});

const { rows } = await pool.query('SELECT NOW()');

Redis with ioredis

const Redis = require('ioredis');

const redis = new Redis(process.env.REDIS_URL || 'redis://127.0.0.1:6379', {
  maxRetriesPerRequest: 2,
  lazyConnect: true,
});
await redis.connect();
await redis.set('greeting', 'hello', 'EX', 60);

Use Redis for caching and short-lived data (sessions, rate limits), not as the only copy of anything important.

Good connection habits

• One pool per process. Create it at start-up and reuse it. Opening a new connection per request exhausts connections and memory.
• Keep pools small. A pool of 3 to 5 connections is plenty for an API on shared hosting.
• Handle errors and retries. Exit with a clear message when start-up connection fails, so the problem is visible in the log.
• Shut down cleanly. Close pools on SIGTERM so restarts do not leave orphaned work.
• Add a health route that runs a trivial query to confirm the database is reachable.

Common errors

To inspect data from your own computer, use an SSH tunnel; see connect to your database over SSH.

Last reviewed 19 October 2026. Need a hand? Contact DignityHost support or open a ticket from your client area.