[keycloak-dev] Sharding and smart proxy

Scaling to a huge amount of load (realms, users and/or sessions) is only going to be feasible through sharding. This could be handled by users themselves by having clusters of clusters, but we could also consider adding this as a built in feature. We could enable sharding at different levels: * Realm * Users * Sessions Then have smart routers that are able to route requests accordingly. We could also enable the option to configure what DCs a specific realm should be replicated to. For example one realm is only replicate to EU, while another to both EU and US. Maybe this could be relatively easy to implement? Not sure, it depends on how much work it would be in the cache layer. We'd also need to implement a smart router. That could probably borrow/share code with a lightweight proxy option.