Multi Tenancy with multiple realms drawbacks

We recently started to move our identity management to Keycloak. We have a SaaS product with users all around the world. Each user belong to a specific tenant with its own permission requirements and login configurations. So users of each tenant need to be able to login to Keyclaok using their SSO. We also use keycloak to define permissions for those tenants as well. So policies for those tenants are also different from each other. We have around 400 tenants and they are going to increase.

My questions are around implications of having tenants within realms.

  • What are the limitations ?

  • Will it have performance effect when number of Realms increase ?

  • What are other alternatives to realms ?

I appreciate your inputs from those who have experience