At least in vCenter 6.5-6.7 developers created nice tiny timebomb. Inside vCenter there are plenty of microservices and they communicate between each other via SSL. And it creates some nice issue with certificate expiration - after certs expire, we'll get only "503". And no vCenter VM restore from backup would help. https://kb.vmware.com/s/article/82332 - to fix it. Usually it's not very convenient to search for help while your cluster management is unavailable, so here's the link upfront.