PHP apps are almost guaranteed to be "stateless", thus scaling up and down is quasi-painless also.
PHP apps are almost guaranteed to be "stateless", thus scaling up and down is quasi-painless also.
When the only place where you can put state is the database then every piece of state is written in the database. Which lead to intelligent individuals (no pun/offense intended) to write clever piece of infra such as Redis. The truth is, for 10 Redis deployment there's 7 (8? 6? Well, a substantial part) where a long living process holding little state would have done the trick. Now you need to deploy, maintain and scale Redis too.
I see downvotes on my GP post, I'm simply stating the fact: if you need state for a building a powerful webapp then obviously there's better runtimes that PHP+Apache, I don't see how one could disagree with that statement, apart from not having sufficient experience in that matter.
There's plenty of good reasons to counterbalance that fact thought, PHP has a very good ecosystem, multiple mature/powerful web frameworks, and cheap/abundant workforce. But it lacks a state holding runtime and for the most demanding applications it's a sufficiently big technical hassle to encourage seeking other runtime and/or language.