Unable to register remote MySQL server: Host is not allowed to connect to this MySQL server

Symptoms

• Only local users are registered in the database server:

  MYSQL_LIN: mysql> SELECT User, Host FROM mysql.user;
  +------------------+-----------+
  | User             | Host      |
  +------------------+-----------+
  | mysql.infoschema | localhost |
  | mysql.session    | localhost |
  | mysql.sys        | localhost |
  | root             | localhost |
  +------------------+-----------+
  4 rows in set (0.00 sec)

• Upon the attempt to register database server in Tools & Settings > Database Servers, the following error is displayed:

  PLESK_ERROR: Error: The test connection to the database server has failed because of network problems:
  
  Host '203.0.113.2' is not allowed to connect to this MySQL server

Cause

'root' user is not allowed to access the database server remotely.

Resolution

Log in to the MySQL on remote database server and create a user which is allowed to access database server remotely from 203.0.113.2:

MYSQL_LIN: mysql> CREATE USER 'root'@'203.0.113.2' IDENTIFIED BY 'root_password';
mysql> GRANT ALL PRIVILEGES ON * . * TO 'root'@'203.0.113.2' WITH GRANT OPTION;
mysql> FLUSH PRIVILEGES;

Or database user which can access the server from any host:

MYSQL_LIN: mysql> CREATE USER 'root'@'%' IDENTIFIED BY 'root_password';
mysql> GRANT ALL PRIVILEGES ON * . * TO 'root'@'%' WITH GRANT OPTION;
mysql> FLUSH PRIVILEGES;