How many does xenforo uses PHP processes simultaneous ? I was receiving the error while i was trying to register test user then i checked logs i saw that then i saw in FPM public pool status this error : So I learnt that my host package ( gandi.net Simple Hosting S pack ) can only 2 php processes( As reminder, a PHP process is the slot that the web server (Apache2) to execute the PHP code/page requested by an user. A PHP process is then opened for a very short time (few millisecond) and freed again. When no PHP processes are available, then the web server Apache2 can't satisfy the client's request asking for a PHP page. So Apache2 fails to respond, and the web accelerator returns the error 503 since no result came from the web server Apache 2 running on Simple Hosting packet).. So my question is what is the minimum req. for xenforo to run properly php process?