I use Gitlab CI for unit testing of a PHP application that talks to a database server. We use a test matrix to test all combinations of versions of PHP and database engines that we support, and have just added MySQL 8.4 to our testing regime. It doesn’t work out of the box with PHP 7.3, but needs mysql_native_password=ON adding to my.cnf. (I appreciate it’s fairly unlikely that someone will use such an old version of PHP in conjunction with a brand new version of MySQL, but the test matrix doesn’t know that.)

At the moment, I have a .gitlab-ci config a bit like this one:

test-php:
  stage: test
  parallel:
    matrix:
      - PHPVERSION: ["7.3"]
        DBSERVICE: ["mysql:8.4"]
  image: php:$PHPVERSION
  services: 
    - $DBSERVICE
  before_script:
    - ./setup-mysql.sh

… and a setup-mysql.sh script that does a bit of database setup, and installs the PHP mysqli extension:

docker-php-ext-install mysqli > /dev/null
docker-php-ext-enable mysqli

if [ "$PHPVERSION" = "7.3" -a "$DBSERVICE" = "mysql:8.4" ]; then
  # PHP 7.3 doesn't support caching_sha2_password authentication
  export DEBIAN_FRONTEND="noninteractive"
  apt-get -qq update && apt-get -qqy install mariadb-client
  mysql -u root -p"$MYSQL_ROOT_PASSWORD" -h mysql 
    -e "ALTER USER '$MYSQL_USER'@'%'
        IDENTIFIED WITH mysql_native_password BY '$MYSQL_PASSWORD'"
fi

Ideally, I would this script also do something like:

cat > /etc/mysql/conf.d/enable-mysql-native-password.cnf <<EOF
[mysqld]
mysql_native_password=ON
EOF

service mysql restart

… but I know that won’t work, as the script is run on the main container, not the MySQL service container. Is there a way of achieving this, while still using standard MySQL image for my service container?