Problem with database!

PDOException: PDO::__construct(): php_network_getaddresses: getaddrinfo for serverdatabase-do-user-18854362-0.g.db.ondigitalocean.com failed: Name or service not known in /var/www/html/class/database.php:8
Stack trace:
#0 /var/www/html/class/database.php(8): PDO->__construct()
#1 /var/www/html/index.php(7): DataBase->__construct()
#2 {main}

Next PDOException: SQLSTATE[HY000] [2002] php_network_getaddresses: getaddrinfo for serverdatabase-do-user-18854362-0.g.db.ondigitalocean.com failed: Name or service not known in /var/www/html/class/database.php:8
Stack trace:
#0 /var/www/html/class/database.php(8): PDO->__construct()
#1 /var/www/html/index.php(7): DataBase->__construct()
#2 {main}