I've found that the realms in keycloak doesn't scale quite as well as we would have wanted.
There is some kind of slowdown, and after around 200 realms things start breaking and startup time starts growing uncontrollably.
There's a good chance it's an issue in our setup (which is fairly complex), but every time we look at it we trace the slowdown back into keycloak itself
Just letting you know it's not you - this is a well known long standing issue with keycloak. Typically users see a significant performance cliff at around 300-400 realms. While one realm is not necessarily the same as one tenant in keycloak, it does make it a significantly larger headache to support multi tenant with SSO integrations in a single realm.
I'm afraid I can't give you more details than that, we just moved on from keycloak at that point.
There is some kind of slowdown, and after around 200 realms things start breaking and startup time starts growing uncontrollably.
There's a good chance it's an issue in our setup (which is fairly complex), but every time we look at it we trace the slowdown back into keycloak itself