Clearly one can write web services in C++. Meta does not really, though. It is Hack code that talks to most web clients (and python for Instagram). The C++ code

Clearly one can write web services in C++. Meta does not really, though. It is Hack code that talks to most web clients (and python for Instagram). The C++ code sits behind that. All of the databases, the caches, the indexing services, the ads ranking and selection are written in C++ and talk Thrift to each other and to the Hack code.