NodeJS ENOTFOUND db when connecting to MySQL container on docker

I am trying to connect From Node.js on Localhost to MySQL instance running on docker using docker-compose.

Node.js gives me this error: ENOTFOUND db, Full error message bellow.

[nodemon] restarting due to changes...
[nodemon] starting `node app.js`
Application Name: RESTFull API - Development
Environment: development
Server is listening on port 3000
getaddrinfo ENOTFOUND db # <------------ Error here
[nodemon] app crashed - waiting for file changes before starting...

Here is docker-compose.yml that contains MySQL and adminer services.

## docker-compose.yml
version: '3.8'

services:
  db:
    image: mysql
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: 'nodejs-restfull-api-development'
    expose:
      - 3306
    volumes:
      - db-config:/etc/mysql
      - db-data:/var/lib/mysql

  adminer:
    image: adminer:latest
    depends_on:
      - db
    environment:
      ADMINER_DEFAULT_DB_DRIVER: mysql
      ADMINER_DEFAULT_DB_HOST: db
      ADMINER_DESIGN: nette
      ADMINER_PLUGINS: tables-filter tinymce
    ports:
      - "8080:8080"

volumes:
  db-config:
  db-data:

Here is my node.js database connection config.

const database = mysql.createConnection({
  host: 'db',
  user: config.get('db.user'),
  password: config.get('db.password'),
  database: config.get('db.database'),
  port: config.get('db.port'),
  connectTimeout: config.get('db.connectTimeout')
});

database.connect(err => {
  if (err) {
    console.log(err.message);
    process.exit(1);
  } else {
    console.log('Connected to database');
  }
});

Answer

You don’t tell us, but I assume your Node app is running on the host and not in a container? If that’s the case, then you need to expose the MySQL port to the host, so it’s reachable. You also need to use localhost as the hostname in your configuration.

Expose the port by changing the database part of your docker-compose file to

  db:
    image: mysql
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: 'nodejs-restfull-api-development'
    ports:
      - 3306:3306
    volumes:
      - db-config:/etc/mysql
      - db-data:/var/lib/mysql

And change your Node configuration to

const database = mysql.createConnection({
  host: 'localhost',
  user: config.get('db.user'),
  password: config.get('db.password'),
  database: config.get('db.database'),
  port: config.get('db.port'),
  connectTimeout: config.get('db.connectTimeout')
});