Azure Availability sets, Fault Domains, and Update Domains

Question

I'm Azure newbie and need some clarifications:

When adding machines to Availability set, in order to prevent VM from rebooting, what's best strategy for VM's, put them in:

-different update and fault domains

-same update domain

-same fault domain ?

My logic is that it's enough to put them in diffrent update AND fault domain

I used this as reference:https://blogs.msdn.microsoft.com/plankytronixx/2015/05/01/azure-exam-prep-fault-domains-and-update-domains/

Am i correct ?

These update/fault domains are confusing

Answer 1

My logic is that it's enough to put them in diffrent update AND fault domain

You are right, we should put VMs in different update and fault domain.

We put them in different update domain, when Azure hosts need update, Microsoft engineer will update one update domain, when it completed, update another update domain. In this way, our VMs will not reboot in the same time.

we put them in different fault domain, when an Unexpected Downtime happened, VMs in that fault domain will reboot, other VMs will keep running, in this way, our application running on those VMs will keep health.

To shot, add VMs to an availability set with different update domain and fault domain, that will get a high SLA, but not means one VM will not reboot.

Hope that helps.