There are not 10,000 other WhatsApps, FWIW. By any useful measure. User base, concurrent active sessions, both of those relative to size of dev team and/or in

There are not 10,000 other WhatsApps, FWIW. By any useful measure. User base, concurrent active sessions, both of those relative to size of dev team and/or infrastructure footprint, acquisition price, user growth rate, etc. Though WhatsApp's success was predicated on dogged adherence to core principles of understanding their problem extremely well, selecting the right tools to solve that problem, and do as much as possible with as little as possible. Erlang was just one part of that. Choosing FreeBSD, not hiring craploads of engineers just for the sake of hiring, keeping as little intermediate state as possible, etc. we're all contributors to their success story. But if you have a high-concurrency, small-packet, low-latency, supreme-uptime message processing shaped problem it's pretty dang hard to do better than Erlang as a foundational choice.