For any reason after rebuilding the container if you are not be able to access MariaDB correctly (i.e. `Access denied for user [...]`) with the previous configuration. Follow these instructions.
Replace `root` with the database root user name, `admin` with the root password, and `db` with the service name specified in the docker-compose `.yml` configuration file. If the connection to the database is successful, then the network configuration is correct and you can proceed to the next step. Otherwise, modify the docker-compose `.yml` configuration file, in the `configurator` service's `environment` section, to use the container names (`frappe_docker-db-1`, `frappe_docker-redis-cache-1`, `frappe_docker-redis-queue-1` or as otherwise shown with `docker ps`) instead of the service names and rebuild the containers.
If you are using old version of `docker-compose` the .env file needs to be located in directory from where the docker-compose command is executed. There may also be difference in official `docker-compose` and the one packaged by distro. Use `--env-file=.env` if available to explicitly specify the path to file.