I’m setting up a local development environment for a WordPress project using Docker Compose, including WordPress, MySQL, and Adminer containers. Here’s my docker-compose.yml file:

version: '3.8'

services:
  wordpress:
    image: wordpress:6
    container_name: wp_dev
    environment:
      WORDPRESS_DB_HOST: ${MYSQL_HOST}
      WORDPRESS_DB_NAME: ${MYSQL_DATABASE}
      WORDPRESS_DB_USER: ${MYSQL_USER}
      WORDPRESS_DB_PASSWORD: ${MYSQL_PASSWORD}
    ports:
      - "8008:80"
    volumes:
      - ./wp-data:/var/www/html

  db:
    image: mysql:5
    container_name: mysql_dev
    environment:
      MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD}
      MYSQL_DATABASE: ${MYSQL_DATABASE}
      MYSQL_USER: ${MYSQL_USER}
      MYSQL_PASSWORD: ${MYSQL_PASSWORD}
    ports:
      - "3305:3306"
    volumes:
      - db_data_dev:/var/lib/mysql

  adminer:
    image: adminer:latest
    container_name: adminer_dev
    ports:
      - "8080:8080"

volumes:
  db_data_dev:

And my corresponding .env file:

MYSQL_HOST=db:3305
MYSQL_DATABASE=wordpress
MYSQL_ROOT_PASSWORD=root
MYSQL_USER=user
MYSQL_PASSWORD=user_pw

However, I’m encountering a connection error between WordPress and MySQL (see screenshot).

Interestingly, when I modify all the environment variables to use the value “wordpress” and remove any port from the MYSQL_HOST variable, the connection works perfectly. Here’s the modified .env:

MYSQL_HOST=db
MYSQL_DATABASE=wordpress
MYSQL_ROOT_PASSWORD=wordpress
MYSQL_USER=wordpress
MYSQL_PASSWORD=wordpress

Can anyone explain why the connection fails when I use different environment variable values and specify a port? Is there something wrong with my setup or configuration?

Any help or insights would be greatly appreciated!

Thank you in advance!

Update:
Thanks to @Dean Ayalon I have understood the problem with the port.
Now my .env file looks like this:

MYSQL_HOST=db # alternativ db:3306
MYSQL_DATABASE=wordpress
MYSQL_ROOT_PASSWORD=root
MYSQL_USER=user
MYSQL_PASSWORD=user_pw

I am still getting the error from the screenshot in this case.