
Explanation:
Box 1: 3
Microsoft has a maximum of 3 fault domains on selected regions.
Box 2: 20
Use 20 for platformUpdateDomainCount
Increasing the update domain (platformUpdateDomainCount) helps with capacity and availability planning when the platform reboots nodes.
A higher number for the pool (20 is max) means that fewer of their nodes in any given availability set would be rebooted at once.
Reference:
https://docs.microsoft.com/en-us/azure/virtual-machines/availability