Unable to open site: 504 Gateway Time-out (nginx), PHP Warning: mysql_connect()

Symptoms

In an attempt to open site example.com the following error appears:

504 Gateway Time-out
nginx

The domain uses FPM application served by Apache or FPM application served by nginx  handler in Plesk > Domains > example.com > PHP Settings and below error can be found in corresponding /var/log/plesk-phpXX-fpm/error.log, where XX – PHP version:

# cat /var/log/plesk-php74-fpm/error.log | grep example.com
WARNING: [pool example.com] child 5833 said into stderr:
“NOTICE: PHP message: PHP Warning: mysql_connect(): Can’t connect to MySQL server on ‘mysql.somehostname.com’ (4) in /var/www/vhosts/example.com/httpdocs/php/connect-mysql.php on line 11”
WARNING: [pool example.com] child 26883 said into stderr: “NOTICE: PHP message: PHP Warning: mysql_connect(): Connection timed out in /var/www/vhosts/example.com/httpdocs/php/connect-mysql.php on line 11”

Cause

MySQL connection settings in the mentioned php file are wrong.

Resolution

1. Login to the server via SSH.
2. Open file specified in /var/log/plesk-phpXX-fpm/error.log . In this case it’s /var/www/vhosts/example.com/httpdocs/php/connect-mysql.php. Find username, its password and host, it can look like below:

   7 DEFINE ('DB_USER', 'user');
   8 DEFINE ('DB_PSWD', 'password');
   9 DEFINE ('DB_HOST', 'mysql.somehostname.com');
   10 DEFINE ('DB_NAME', 'database');
   11 $conn = mysql_connect(DB_HOST,DB_USER,DB_PSWD) or die("error to connect server");

3. Check that  parameters DB_USER, DB_PASSWORD and DB_NAME are correct. It must be possible to connect to database:

   # mysql -u “user” -p “password” “database” -h “mysql.somehostname.com”

   If the command above fails with the next error:

   # mysql -u “user” -p “password” “database” -h “mysql.somehostname.com”
   ERROR 1045 (28000): Access denied for user ‘user’@’localhost’ (using password: YES)

   then some of parameters user, password, database are not correct. Verify them and change if necessary.

   Note: If database was created in Plesk user and password can be changed in Plesk > Domains > example.com > Databases