[nickserv]

It's certainly possible, but more complex than just putting up a bunch of stateless application servers all accessing the same database. With no local cache. Then saying the DB is slow ;-)

It's also the kind of thing many developers don't like doing: thinking about operational concerns.

As an aside, horizontal scaling of sorts can be achieved by using microservices, it's actually one of the few really valid reasons for this type of architecture. If the microservice databases are not independent, you're doing it wrong.