Do you know of a good explanation for fault domains and update domains?

Question

I'm new to Azure and have been struggling with a concept specifically update domains and fault domains. Probably having a harder time understanding Update Domains. So as I understand it, having 3 VMs in 3 fault domains would be essentially having those VMs spread out to three racks? Is that correct? Like this

Fault domain 1	Fault domain 2	Fault domain 3
VM 1	VM 2	VM 3

If that is wrong, please correct me. So then what is an update domain? A lot of the documentation I have seen shows a demonstration for the fault domain similar to the table above and will describe what kind of sounds like the fault domain. If you have a link to a good explanation that would be a big help or if you think you could dumb it down for me a bit, that would work too.

Answer 1

Under certain circumstances, two VMs in the same availability set might share a fault domain. If all the servers part of fault domain are restarted there is fair chance of your application going down if fault domain is restarted.

Answer 2

Each virtual machine in your availability set has an update domain and fault domain assigned. Fault domains indicate the group of virtual machines that share common power source and network switch limiting the impact of potential physical hardware failures, network outages, or power interruptions. Update domains indicate the group of virtual machines and underlying physical hardware that can be rebooted at the same time ensuring availability of some virtual machines during a planned maintenance. Link: https://learn.microsoft.com/bs-latn-ba/azure/virtual-machines/availability-set-overview#how-do-availability-sets-work