Simple method to override configuration for your MySQL container

First approach : wrong one

All started while I was doing another dumb import, first using PhpMyAdmin. Despite the fact than the file wasn't particularily large, it keeped ended by error MySQL server has gone away with a strange mention to missing data close to an ON directive.

Few searches quickly pointed me on configuration directive max_allowed_packet. If too short, it indeed leads to above error. Beware the packet size here refers to a TCP packet, on transport layer. Too large query can trigger this.

As I use my stack for making project live on local, I first thought that I would have to overkill stuff by making custom image from MySQL one, with overriding my.ini, exactly as I did for PHP container.

Then I realized that exactly like PHP and Apache, a conf.d folder was existing with MySQL folder architecture.

Lightweight approach

So the solution was quite easier : just define a override_max_packet_size.cnf (you name it like you want), that lies in docker/images/mysql/conf. I put this inside :

[mysqld]
max_allowed_packet=64M

Then just mount a volume targeting this host folder and bind it with /etc/mysql/conf.d

services:
  mysql:
    env_file: ./.env
    image: mysql:5.7
    ports:
      - ${MYSQL_HOST_PORT}:${MYSQL_PORT}
    environment:
      MYSQL_DATABASE: ${MYSQL_DATABASE}
      MYSQL_USER: ${MYSQL_USER}
      MYSQL_PASSWORD: ${MYSQL_PASSWORD}
      MYSQL_ROOT_PASSWORD: ${MYSQL_PASSWORD}
    volumes:
      - ${MYSQL_HOST_VOLUME_PATH}:/var/lib/mysql
      - ./docker/images/mysql/config:/etc/mysql/conf.d

Complete stack rebuild, and try to reimport : bingo, it works. Using this method, you can safely override any MySQL configuration directive while keeping image untouched.