Docker MYSQL '[2006] MySQL server has gone away' - mysql

Question

i have a little problem with mysql server.
i created my docker-compose.yml, but when i want to access to phpMyAdmin (localhost:8080), an error message appeared sais that:
"phpMyAdmin tried to connect to the MySQL server, and the server rejected the connection. Please check the values ​​of host, username and password in the configuration and make sure they match the information provided by the MySQL server administrator".
Here is my docker-compose file and thanks for helping me
version: '2'
services:
apache:
image: rafaelcgstz/magento2
# build: .
ports:
- 80:80
- 9001:9000
# - "35729:35729" # live reload
volumes:
- ./src:/var/www/html
- ~/.composer:/var/www/.composer
- ~/.npm:/var/www/.npm
# - ~/.nvm:/var/www/.nvm
environment:
XDEBUG_CONFIG: "remote_host=localhost"
PHP_IDE_CONFIG: "serverName=Docker"
depends_on:
- db
links:
- db
networks:
- magento-network
db:
image: mariadb
ports:
- 3300:3306
environment:
- MYSQL_ROOT_PASSWORD=root
- MYSQL_DATABASE=magento
- MYSQL_USER=magento
- MYSQL_PASSWORD=magento
volumes:
- dbdata:/var/lib/mysql
networks:
- magento-network
phpmyadmin:
image: phpmyadmin/phpmyadmin
environment:
- PMA_HOST=db
- PMA_USER=root
- PMA_PASSWORD=root
- MYSQL_ROOT_PASSWORD=root
ports:
- 8080:80
networks:
- magento-network
redis:
image: redis
ports:
- 6379
networks:
- magento-network
redis-session:
image: redis
ports:
- 6379
networks:
- magento-network
mailhog:
image: mailhog/mailhog
ports:
- 1025:1025
- 8025:8025
networks:
- magento-network
networks:
magento-network:
driver: bridge
volumes:
dbdata:
driver: local

Answer 1

Seems like you have a typo in mariadb service definition:
ports:
- 3300:3306
You configured port mapping so that container is reachable at 3300 but you did not pass this information to PHPMyadmin. As a result connection attempt just times out.
Side note: you do not need to expose port for database at all - other containers will communicate with it using Docker's virtual network and for local access you can use docker container -it exec <container-id> mysql... or docker-compose exec db mysql...

Answer 2

while it appears there is a typo for the port with this post I want to point out that it's important to make sure that your user has access 'TO' and 'FROM' the appropriate IP.
This is an (wide open -adjust as needed) example for updating the access domain when running adminer / phpadmin via docker:
GRANT ALL ON . TO 'admin'#'172.18.0.0/255.255.255.0' IDENTIFIED BY 'password' WITH GRANT OPTION;
p.s. I'm adding this answer here because I also landed on this page with the same error.

Answer 3

I solved my problem with this command:
docker-compose destroy
sudo rm -rf db/
docker-compose up -d
docker-compose web
composer install
symfony d:m:m --no-interaction
symfony d:f:l --no-interaction