MySQL connection from docker container php:8.1.17-apache to docker container mysql:8.0.32 doesn't work – PHP Versions

There is a lot to unpack here.

1. Consider each docker-compose.yml a different "project". For each project docker-compose will create its own virtual network. Without additional config in each project those virtual networks will not be able to talk to each other

2. The declarations in the ports: section will map the port out to the host machine’s localhost:port but that is it.

   • Note: actually ALL interfaces will now be listening on that port, not just local.

3. "localhost" is only local to the individual container. Each container has its own, and none of them are the host machine’s "localhost" either.

4. Most mysql drivers [including PHP’s] map the name localhost to the local unix socket which is only available if you’re running the code on the same host [or container, in this case] as Mysql.

#4 is why you’re getting the quizzical "file not found" error on connection, because it can’t find the socket file, and everything else is why it wouldn’t have worked anyway.

The simple solution is to combine the two services into a single docker-compose.yml and then use the mysql service’s hostname instead of localhost.

version: '3.8'

services:
  vidslide-api:
    image: php:8.1.17-apache
    ports:
      - "80:80"
    volumes:
      - ./htdocs:/var/www/html
    command: >
      sh -c "
      docker-php-ext-install mysqli && 
      docker-php-ext-enable mysqli && 
      apache2-foreground
      "
  vidslide-db:
    image: mysql:8.0.32
    command: --default-authentication-plugin=mysql_native_password
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: ***
    ports:
      - "3306:3306"
    volumes:
      - /var/lib/vidslide_mysql-db:/var/lib/mysql
volumes:
  mysql_data: 

Docker-compose creates local DNS names for each service, so your mysql hostname will be vidslide-db instead of localhost.

Additionally, you don’t want to be installing anything every time your container starts, unless you really like waiting for extensions to compile every time the container starts. For this you’ll want to build your own image that includes this, and Docker-compose makes it easy to build on demand.

Add this as Dockerfile-php in the same dir as your docker-compose.yml:

FROM php:8.1.17-apache

RUN docker-php-ext-install mysqli && 
    docker-php-ext-enable mysqli

And change the vidslide-api service to simply:

  vidslide-api:
    build:
      dockerfile: Dockerfile-php
      context: ./
    ports:
      - "80:80"
    volumes:
      - ./htdocs:/var/www/htm