Azure Virtual Machines — Trivia & Quick Facts¶

Terse, quiz-worthy facts about Azure VMs — specific numbers, limits, and defaults worth memorizing.

A subscription has both total regional vCPU quota and per-family regional vCPU quota; deployments must satisfy both.
An availability set supports up to 3 fault domains and 20 update domains, fixed at creation.
A VMSS orchestration mode (Flexible vs. Uniform) cannot be changed after the scale set is created.
Supported VMSS configurations can scale to 1,000 instances; some older image paths have lower ceilings.
Stopped and Stopped (deallocated) are materially different billing/allocation states — only the latter stops compute billing.
Deallocated VMs still incur charges for managed disks and other retained resources.
A temporary disk is local, non-durable storage and may disappear after host-level operations (redeployment, resize, maintenance).
Ephemeral OS disk VMs do not support normal stop-deallocate and later resume.
Azure Managed Disks are encrypted at rest by default with platform-managed keys unless another supported encryption design is selected.
Disk performance is constrained by both the disk SKU/size limits and the VM size's aggregate limits — whichever is lower wins.
Spot VMs can be evicted for capacity or price reasons; there is no availability SLA.
A system-assigned managed identity is deleted with the VM; a user-assigned identity survives independently and is reusable across resources.
cloud-init runs during first boot and is supported for Linux VMs and Flexible scale sets.
Availability Zones protect against datacenter-level failure; availability sets do not provide regional or zone-level DR.
Capacity reservation and reserved-instance (billing discount) pricing are separate concepts — one guarantees capacity, the other only discounts price.