Websites show 502 Bad Gateway and Apache cannot be started: DocumentRoot must be a directory

Symptoms

1. Websites are showing 502 Bad Gateway

2. Apache is stopped and fails to start with the following message:

   # service httpd start
   Starting httpd: Syntax error on line 16 of /etc/httpd/conf/plesk.conf.d/server.conf:
   DocumentRoot must be a directory
   [FAILED]

   or with the following one:

   # service httpd start
   Starting httpd: Syntax error on line 16 of /etc/httpd/conf/plesk.conf.d/server.conf:
   DocumentRoot '/var/www/vhosts/default/htdocs' is not a directory, or is not readable
   [FAILED]

Cause

Default document root is missing or has incorrect ownership.

Resolution

1. Connect to the server via SSH.

2. Find path to document root in /etc/httpd/conf/plesk.conf.d/server.conf file.
   By default it is set as /var/www/vhosts/default/htdocs:

   # grep 'DocumentRoot' /etc/httpd/conf/plesk.conf.d/server.conf
   DocumentRoot "/var/www/vhosts/default/htdocs"

3. Check if the directory exists on a server:

   # ls -ld /var/www/vhosts/default/htdocs
   ls: cannot access /var/www/vhosts/default/htdocs: No such file or directory

4. Create directory if it is missing:

   # mkdir /var/www/vhosts/default/htdocs

5. Set correct ownership:

   # chown root:root /var/www/vhosts/default/htdocs

6. Start Apache:

   # service httpd start

Note: if the directory is different in the path, do the same for it.