"Service Unavailable" error on website with alt-php in MultiPHP Manager

Symptoms

The website shows a 503 "Service Unavailable" error when using ALT-PHP in the MultiPHP Manager with PHP-FPM enabled.

Cause

Using ALT-PHP versions doesn't automatically enable or start the PHP-FPM service. This is generally disabled because it is not the recommended option on CloudLinux servers. 

Resolution

The recommended PHP handler for ALT-PHP versions on CloudLinux is LSAPI. To make use of ALT-PHP options on CloudLinux servers, you also must use the PHP Selector interface.

In the MultiPHP interface, set the PHP version to the "inherit" option, then use the PHP Selector to set the Alt-PHP version.

Using the MultiPHP Manager with CloudLinux's PHP Selector