Upgrade first, link afterwards.
Installation order is crucial!
- Install SSO on vCenter A, upgrade Inventory Service A, upgrade vCenter Server A.
- Export SSO configuration.
- Install SSO on vCenter B, import SSO configuration from vCenter A, upgrade Inventory Service B, upgrade vCenter Server B.
- Export SSO configuration from vCenter B
- Import this in the SSO of vCenter A
- Link both vCenter Servers