Azure – Can Azure availability set span 2 regions (Dublin, Amsterdam)

I had the same problem today. The only way I could bypass this was:

1. Create a new web application on https://portal.azure.com
2. Change "Application Insights" in Monitoring Section of the new web app to force it to one of the available zones (in dropdown list)
3. Export the publishing setting for this web app
4. In Visual studio, publish the application importing the above publishing settings instead using Azure publishing options

While I have yet to find official Microsoft documentation on this topic, there is some information buried in documentation issue discussion.

For example, on Issue 39091, a Microsoft rep has stated:

There is basically an ‘Allocator’ that makes decisions based on a variety of factors including capacity, health etc but from a customer perspective yes, they have no say in what DC is chosen.

I believe that Zonal resources placed without a zone specified are allocated according to internal private logic, and upon de-allocation and re-allocation, can be moved or placed as that "allocator" desires.

To answer your second question, it isn't possible for a data disk to be placed in a different zone than it's VM. If a VM exists in Zone 1, and you create a data disk in Zone 2, you cannot attach that data disk. I can only assume (finding no direct confirmation) that when you create a VM and disk together, the "allocator" will always place them in the same zone.