Question about high availability/load balancing

Hello,

I have 8 identical servers that I need to use to run 4 different types of
servers. I would like to set up 4 clusters of 2 servers each to accomplish
this. Ideally, I'd like each cluster to provide high availability as well as
load balancing. However, it seems that all the topology diagrams for
providing both these services necessitate 4 machines - a primary router, a
backup router and 2 "real servers" to do the actual work.

Which brings me to my question: is it possible/feasible to set up clusters
of two machines in each, in which each machine is acting both as a router
and as a "real server," in order to provide both load balancing and high
availability? Or could I have one set of two routers that manage servers in
4 different clusters?

Thanks in advance.

Regards,
Martin Goldman