> No, I mean, if you're WhatsApp - across all nodes - then somehow maybe yes?

I mean, we had one process per client connection (which is 100% the way to go) and depending on the era, hundreds of thousands or millions of connections per chat node. I don't think we ever really summed the number of processes over a cluster.

Other than client processes, there weren't that many processes per node; like you say, it doesn't make sense to spread too thin.

There's a lot of client connections and so a lot of client processes, but it ends up being pretty simple to work with them. They all do the same thing... wait for a message, process the message, wait some more. Some of the messages are tricky to process (like the user just logged in again over here, so please transfer the state)