I have many resources (App Services, SRV, VMs, Storage, LB, analytics, etc) in Azure and I'm looking to have them in availability zone. But I'm considering limitations.
So far, I have discovered that not all VM sizes are supported and not all regions are supported.
Are there other limitations, even those that are yet to be documented?
About the limit of the Azure Availablility Zone, you can have a look of this doc:
https://learn.microsoft.com/en-us/azure/availability-zones/az-overview#services-support-by-region
Only specfic combinations of Azure services and regions support Availability Zones.
For each service that supports Availability Zones, there are some things to note:
1, For virtual machines, pay attention to whether the virtual machine size is available in the area you need.
2, For virtual machine scale set, you need to be aware that when you deploy a scale set into one or more zones, you have the option to deploy with "max spreading" or "static 5 fault domain spreading". With max spreading, the scale set spreads your VMs across as many fault domains as possible within each zone. This spreading could be across greater or fewer than five fault domains per zone. With "static 5 fault domain spreading", the scale set spreads your VMs across exactly five fault domains per zone. If the scale set cannot find five distinct fault domains per zone to satisfy the allocation request, the request fails.
3, For databases, Zone redundant databases and elastic pools are currently only supported in the Premium and Business Critical service tiers in select regions. When using the Business Critical tier, zone redundant configuration is only available when the Gen5 compute hardware is selected. And This feature is not available in Managed instance.
4, For Azure Event hub, geographic disaster recovery related to Availability Zones is only available for the standard and dedicated SKUs.
5, For Azure Service Bus, this feature is available for Service Bus Premium SKUs and only ensures that metadata (queues, topics, subscriptions, filters) is copied from the primary namespace to the secondary namespace during disaster recovery when pairing.