You plan to move a distributed on-premises app named App1 to an Azure subscription. After the planned move, App1 will be hosted on several Azure virtual machines. You need to ensure that App1 always runs on at least eight virtual machines during planned Azure maintenance. What should you create? 

Answer options:

A. one virtual machine scale set that has 10 virtual machines instances
B. one Availability Set that has three fault domains and one update domain
C. one Availability Set that has 10 update domains and one fault domain
D. one virtual machine scale set that has 12 virtual machines instances

C

An update domain is a logical group of underlying hardware that can undergo maintenance or be rebooted at the same time. As you create VMs within an availability set, the Azure platform automatically distributes your VMs across these update domains. This approach ensures that at least one instance of your application always remains running as the Azure platform undergoes periodic maintenance. Reference: http://www.thatlazyadmin.com/azure-fault-update-domains/