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

I am using sequelize, MySQL and docker together for the first time and cannot get sequelize to connect to the db.

I have tested the presence of the DB with DBeaver and I can connect. I can also see the MySQL container respond in the terminal when I connect via DBeaver. However, when attempting to connect with code I get an ECONNREFUSED error.

I have checked my code with the sequelize docs and double checked port settings but cannot seem to see where I am going wrong.

After the correct answer was provided below I noticed that I had a bug. I missed the following from the ‘mysql’ container in the docker-compose.yml file.

networks:
    - app-tier

To avoid requiring other users to read the comments in the answer to discover this, I have added this to the docker-compose.yml file so that the question and answer now align more clearly

docker-compose.yml file:

version: '3'

networks:
    app-tier:
        driver: bridge
services:
    server:
        image: bitnami/node
        networks:
        - app-tier
        command: "sh -c 'npm install && npm run dev'"
        volumes:
        - ./server:/app
        ports:
        - 5000:5000
        depends_on:
        - mysql
    mysql:
        image: 'bitnami/mysql:latest'
        environment:
        - MYSQL_USER=root
        - MYSQL_PASSWORD=password
        - MYSQL_ROOT_PASSWORD=password
        - MYSQL_DATABASE=school
        networks:
            - app-tier
        ports:
        - '3306:3306'
        volumes:
        - ./db:/bitnami/mysql/data

Sequelize connection:

const Sequelize = require('sequelize');

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

module.exports = sequelize;

Attempt to sync from app.js:

sequelize.sync()
    .then(result => console.log(result))
    .catch(err => console.log('EEEERRRROOOOOOR',err));

Terminal output:

server_1    |  { SequelizeConnectionRefusedError: connect ECONNREFUSED 127.0.0.1:3306
server_1    |     at Utils.Promise.tap.then.catch.err (/app/node_modules/sequelize/lib/dialects/mysql/connection-manager.js:139:19)
server_1    |     at tryCatcher (/app/node_modules/bluebird/js/release/util.js:16:23)
server_1    |     at Promise._settlePromiseFromHandler (/app/node_modules/bluebird/js/release/promise.js:512:31)
server_1    |     at Promise._settlePromise (/app/node_modules/bluebird/js/release/promise.js:569:18)
server_1    |     at Promise._settlePromise0 (/app/node_modules/bluebird/js/release/promise.js:614:10)
server_1    |     at Promise._settlePromises (/app/node_modules/bluebird/js/release/promise.js:689:18)
server_1    |     at Async._drainQueue (/app/node_modules/bluebird/js/release/async.js:133:16)
server_1    |     at Async._drainQueues (/app/node_modules/bluebird/js/release/async.js:143:10)
server_1    |     at Immediate.Async.drainQueues (/app/node_modules/bluebird/js/release/async.js:17:14)
server_1    |     at runCallback (timers.js:810:20)
server_1    |     at tryOnImmediate (timers.js:768:5)
server_1    |     at processImmediate [as _immediateCallback] (timers.js:745:5)
server_1    |   name: 'SequelizeConnectionRefusedError',
server_1    |   parent:
server_1    |    { Error: connect ECONNREFUSED 127.0.0.1:3306
server_1    |     at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1191:14)
server_1    |      errno: 'ECONNREFUSED',
server_1    |      code: 'ECONNREFUSED',
server_1    |      syscall: 'connect',
server_1    |      address: '127.0.0.1',
server_1    |      port: 3306,
server_1    |      fatal: true },
server_1    |   original:
server_1    |    { Error: connect ECONNREFUSED 127.0.0.1:3306
server_1    |     at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1191:14)
server_1    |      errno: 'ECONNREFUSED',
server_1    |      code: 'ECONNREFUSED',
server_1    |      syscall: 'connect',
server_1    |      address: '127.0.0.1',
server_1    |      port: 3306,
server_1    |      fatal: true } }

Source: StackOverflow