Sequelize cannot sync to MySQL in a docker container from Node/express app (ECONNREFUSED)

To connect to your mysql server from a docker container you need to pass a proper service address. So your initialization should look like this.

const Sequelize = require('sequelize');

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

module.exports = sequelize;