How to connect to a database using Docker?

Question

PHP

Wrote a `docker-compose` file with the following content:

version: '2'

services:
  php:
    image: chialab/php:7.3-fpm
    container_name: exchange-php
    working_dir: /app
    volumes:
      - .:/app
    environment:
      - APP_ENV=test

  mysql:
    image: mysql:5.7
    container_name: exchange-mysql
    volumes:
      - './docker/mysql/my.cnf:/etc/mysql/my.cnf'
    ports:
      - 33060:3306
    environment:
      - MYSQL_ROOT_PASSWORD=root
      - MYSQL_DATABASE=test_db
      - MYSQL_USER=test_user
      - MYSQL_PASSWORD=test_password

I want to connect to the database:

docker exec exchange-php php -r "new PDO('mysql:host=exchange-mysql;port=33060;charset=utf8', 'test_user', 'test_password');"

I get an error: `SQLSTATE[HY000] [2002] Connection refused`
I go into the mysql container and check if mysql is listening on all IPs:

$ docker exec -it exchange-mysql bash
$ mysqld --verbose --help | grep bind-address

  --bind-address=name IP address to bind to.
bind-address                                                 0.0.0.0

I also checked that the user is allowed to authorize:

mysql> SELECT host, user FROM mysql.user;
+-----------+---------------+
| host      | user          |
+-----------+---------------+
| %         | root          |
| %         | test_user     |
| localhost | mysql.session |
| localhost | mysql.sys     |
| localhost | root          |
+-----------+---------------+
5 rows in set (0.00 sec)

What needs to be done to connect to mysql using php and docker?