"core bussiness" is finding and dispatcching drivers including payments. Everything in-app.
> I can't imagine trying to deal with 1m+ concurrent tcp connections.
2 million connections on a BSD mchine is doable though not trivial and that too even in 2012.
https://blog.whatsapp.com/1-million-is-so-2011
> I can't imagine trying to deal with 1m+ concurrent tcp connections. 2 million connections on a BSD mchine is doable though not trivial and that too even in 2012. https://blog.whatsapp.com/1-million-is-so-2011