When running App1 on seven Azure virtual machines in an Availability Set, how many instances will remain available during planned maintenance if fault domains are set to 3?

In an Azure Availability Set, virtual machines (VMs) are distributed across fault domains. Fault domains are essentially racks of hardware that provide physical separation of VMs, ensuring that if there is a hardware failure or planned maintenance that affects one domain, the other fault domains will still be operational.

Given that there are three fault domains and you have a total of seven VMs in an Availability Set, Azure will allocate the VMs across these fault domains. This means that each fault domain will ideally host an approximately equal number of VMs to minimize the risk of simultaneous failures across all VMs.

When planned maintenance occurs, Azure typically takes down VMs in one fault domain at a time. With three fault domains, it is important to calculate how many VMs can remain operational during that planned maintenance.

In this scenario, if VMs are evenly distributed among the three fault domains, you could expect that each fault domain will host at least two VMs, with one fault domain potentially hosting an additional VM. Therefore, if one fault domain is taken offline for maintenance, the remaining two fault domains would still have their VMs operational.

Following this logic, during planned maintenance, up to four VMs (two from each of two fault domains) can remain