Memory hook: Size for the bottleneck, place for failure and distinguish stopped from deallocated.
Must remember
- Choose VM family/size using CPU, memory, storage throughput, networking and compatibility. Availability differs by Region and quota. Resizing may require restart/deallocation or a compatible host allocation; check disk and NIC limits too.
- Managed disks have performance and redundancy options. OS disks, data disks and temporary disks have different purposes; temporary storage is not durable business data. Snapshots capture disk state, but application consistency may require additional coordination.
- Availability sets distribute supported VMs across fault/update domains; availability zones distribute across zonal failure domains. A VM Scale Set manages a group of instances with selected orchestration, upgrade and autoscale behaviour. Health probes and application readiness affect safe replacement.
- Stopped within the guest can leave compute allocated and billed; deallocated releases allocation, though retained disks, snapshots and other resources can still bill. Public/private address behaviour depends on address configuration and lifecycle.
- Encryption at host protects supported host-side storage paths; disk encryption and guest/application encryption solve related but distinct requirements. Use trusted boot/security features where the workload and VM generation support them.
- Moving a resource group/subscription is a management-scope operation; moving to another Region generally involves a supported relocation/redeployment process. Validate dependencies, identity/role assignments, network addresses, extensions and backup settings after any move.
- Use Bastion or appropriate controlled administration paths. VM extensions and cloud-init/custom-data mechanisms help configure guests, but failed bootstrap scripts need logs and exit-status investigation. Never assume the portal's running state means the app is ready.
Choose under exam pressure
| Requirement | Choice and reason |
|---|---|
| Scale a replaceable VM fleet | VM Scale Sets with health-aware policy. |
| Survive a zone loss | Sufficient working capacity across zones and resilient state. |
| Stop paying for allocated compute during a pause | Deallocate, then account for retained resources. |
Traps
- Guest shutdown and deallocation differ.
- Temporary disk data must be reproducible.
- A Region move is not merely changing a resource-group label.
Active recall
1. Which retained VM resource can bill after deallocation?
Managed disks and snapshots, among other independent resources.
2. What protects against an AZ failure: two VMs in one zone or spread across zones?
Spread across zones with the necessary application/dependency capacity.
3. Why can resizing fail despite a valid SKU?
Quota, regional/zone capacity, host compatibility or resource limits.
4. Does a disk snapshot prove application consistency?
No. Coordinate the application or use an appropriate backup mechanism.
5. What should an autoscale signal represent?
Useful demand or saturation that additional instances can actually relieve.