I've been down this road a bit, though actually in Docker Swarm. One aspect I spend a lot of time digging into was running multiple keycloak containers with shared cache. On metal or a VM with multicast, they'll find each other no problem, and it works beautifully, but I'm not aware of any container orchestration that brings multicast out of the box (and I don't think AWS does either). Keycloak has a built in Kubernetes DNS discovery mechanism to find its peer containers and share cache which also worked quite well on Swarm, though I lost a day or two tweaking it.
Yes, Keycloak cluster works fine on Kubernetes. It takes some time to read all the docs and understand things, but nothing outrageous, that was my experience at least.
Curious - I've seen several references that it doesn't support it, and that keycloak has a dedicated ec2 cache discovery option. But I don't use AWS anyway, so I'm far from knowledgable about it.
