There are libraries and frameworks.

Note that before Java adoption push we had stuff like ATLServer, and the first version of ASP were basically COM libraries being called from VBscript/JScript.

On our case, we were calling C code from TCL scripts, using plugins like mod_tcl.

Nowadays you have stuff like Boost ASIO and Wt.

However I wouldn't plug C or C++ directly into the Internet, rather call them from managed languages, as native libraries, reducing the risk of possible exploits.

This is what I had considered to be the state of things. The phrasing on initial read suggested to me that C++ & Rust were the default now for performance critical services (with Rust being a new add) and Hack was used where it made sense but not necessarily by default anymore. I think I may have discounted Hack's role too much.

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.

> How would one go about building a rest service in C++?

I'd use https://github.com/drogonframework/drogon if the app needs to be pure C++ or Cutelyst (https://cutelyst.org/) if it's a Qt app which needs to expose an http server

I haven't built anything serious with it, but cpp-httplib is a very easy-to-use framework for processing HTTP requests.

"backend" does not necessarily means the part that receives the HTTP request from the client. It could be a microservice that speaks some other protocol, a load-balancer that sits in front of the web workers, and task runner, etc.

> How would one go about building a rest [service.]

At Meta, you wouldn't. Everything is Thrift. For WWW, you'll have more graphql.

Meta also has a shit ton of libs to make service development easier than exists publicly.

If you have organizational backing, it is not hard to use C++ because the company would have already standardized on libraries like Boost and Folley.

And the company would already have a build farm.

I’d bet they use e.g. Python to receive the HTTP calls and do basic logic at that level, but use C++ libs to chew through lots of multimedia, ML/AI, etc.

Check out WebAssembly.