I have questions about how you load balance in the cluster.
depends on your configuration and cache storage, varnish and redis
one server for cache and other servers connected to this one
As I understand it, if you have a Magento cluster, clustering the cache is nearly impossible if you try to load balance too?
So you either have it load balanced or you have it clustered, but both is not possible?
I think the terms 'clustering' and 'load balancing' is somewhat confusing - I do believe you mean the same thing in this context and, it's entirely possible to have Magento cached using Nginx + Varnish in a clustered environment.
Are you wanting to do multi-master replication of your database and caching layer or simply load balance the web servers?
Cache and Web server both clustered and load balanced at both layers.
there is multiple ip dns, or one entry point, but
both varnish and redis support clustering, sharding, failover and load balancing
still not sure what are you looking for?
varnish and redis are well documented