Docker MYSQL '[2002] Connection refused'

The '[2002] Connection refused' means you can reach the database server, but you don't have right access for the user (in your case admin). By default mariadb have a root user with the password given by MYSQL_ROOT_PASSWORD and this user can connect from any server (%).

If you want use an over login to your databases, you have to create it in the databases server with the right granting on databases from chosen locations.

The problem here is that you have named your database server as 'mysql' (service name in the docker-compose file). But by default phpmyadmin tries to connect to a database server named 'db'. Adding PMA_HOST: mysql under the environment section of the phpmyadmin service will resolve this problem.

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I think that MYSQL_USERNAME and PMA_ARBITRARY are useless if you work with default configuration (connection with root to your databases server)

In my case I was running mysql in a docker container whose port was mapped to the host mac (3306:3306). I tried connecting to this database from a phpmyadmin docker container using 127.0.0.1 . But it won't work because the localhost on the phpmyadmin docker container does not have the required mysql running.

To connect to the host from docker network

docker.for.mac.host.internal

Docker Networking Docker Compose Networking

I had this challenge because I am running 3 different containers with different IP Addresses

db - 172.18.0.3 - container for MYSQL
app - 172.18.0.2 - container for Laravel app

so I fixed it by editing my Laravel .env file

DB_CONNECTION=mysql
DB_HOST=172.18.0.3
DB_PORT=3306
DB_DATABASE=database_name
DB_USERNAME=username
...

To get your containers Ip addresses. From your docker host

docker inspect -f '{{.Name}} - {{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' $(docker ps -aq)

UPDATED: For latest docker versions and based on the services name, "mysql", in your docker-compose.yml

mysql:
  image: mariadb
  ports:
    - 3306:3306

You can try this:

DB_CONNECTION=mysql
DB_HOST=mysql
DB_PORT=3306
DB_DATABASE=database_name
DB_USERNAME=username

DB_HOST is the name of MySQL service name defined in docker-compose.yml

I've managed to connect to the mysql instance using mysql command line tool, this is the command I used - mysql -u root -p -h 127.0.0.1, and the entering the admin password. Is that a sufficient solution for you?