Keycloak supports deployments that consist of multiple Keycloak instances that connect to each other using its Infinispan caches; load balancers can distribute the load evenly across those instances. Those setups are intended for a transparent network on a single site.
The Keycloak high-availability guide goes one step further to describe setups across multiple sites. While this setup adds additional complexity, that extra amount of high availability may be needed for some environments.
The different guides introduce the necessary concepts and building blocks. For each building block, a blueprint shows how to set a fully functional example. Additional performance tuning and security hardening are still recommended when preparing a production setup.