There are many reasons which lead to a cleaner codebase, some of them are: RAII, smart pointers, constant types, reusable containers, standard algorithms library, cleaner way to define interfaces, etc.

Overall our experience is that C++ code is smaller, simpler to write/read, and has a smaller chance of mistakes than equivalent logic written in C.

Of course many of this points are relevant only for relatively modern C++ (c++11/c++14 or newer), before that the cost/benefit ratio was much less clear.

I'm not declaring that C++ is better for everything. In our case it is better because it makes this part of the infrastructure more sustainable: there are more engineers who can code well in C++ vs C in our company and industry overall. Also it is easier to code in C++ as it is general purpose programming language with a lot of libraries available, open source projects, community around it etc.

I think what they're trying to say is that developing plugins for nginx in Lua is not great. It's not a rant about languages.

This has to do with nginx not having the required features (features blocked behind the paid edition or GRPC non existent), forcing to develop plugins in Lua to compensate (the only supported language) and Lua is too slow for this sort of stuff (processing Gbps of traffic in real time is no joke).