Unable to open any domain with enabled nginx on Plesk because Apache is not running

Plesk for Linux kb: technical ABT: Group B

Applicable to:

Unable to browse any domain hosted on the Plesk server. The browser displays this error:

CONFIG_TEXT: 502 Bad Gateway
Nginx reverse proxy is enabled in Tools & Settings > Services Management.
Nginx service is running.

Apache service is stopped on the server.

Click on a section to expand

Via Plesk GUI

Log in to Plesk GUI
Go to Tools & Settings > Services Management > Apache Web Server > Start.
If the issue remains the same (or sites are not working with the different error message), go to Extensions > My Extensions > Webserver Configuration Troubleshooter and Rebuild All configuration files:

Via command-line interface

Connect to the server via SSH
Start Apache Web Server:
1. For CentOS based:
  
  # service httpd start
2. For Debian based:
  
  # service apache2 start
If the issue remains the same (or sites are not working with the different error message), execute the following command:

# plesk repair web -y