Peter Hintjens wrote a lot of different protocols in https://zguide.zeromq.org/docs/chapter4/#Service-Oriented-Re... and they mostly are part of the spec https://rfc.zeromq.org/spec/18/ now.

Some of these protocols are a good improvement when looking for the ultimate in speed and I used them where applicable, but as a first order approximation a simple load balancer approach is quite good enough. Especially when you do not have dedicated people vested in that domain for maintenance.