/azure-compute

Capacity Reservation Overview

Reference material for Azure Capacity Reservation Groups and Capacity Reservations.

What Is a Capacity Reservation Group?

A Capacity Reservation Group (CRG) is a logical container for one or more capacity reservations. It acts as the association point for VMs and VMSS — you associate a VM or scale set with the group, and Azure matches the VM to a suitable reservation within that group.

Constraints

Association and Disassociation

See association-disassociation.md for how to associate and disassociate VMs/VMSS with a CRG.

Common CLI Commands

Finding Valid CRGs for a VM

To associate a VM with a CRG, the CRG must contain a capacity reservation that matches the VM's size, region, and zone (if zonal). While az capacity reservation group list can enumerate CRGs at the subscription level, filtering down to matching reservations across many groups is inefficient. Azure Resource Graph is recommended for cross-resource-group discovery.

Option 1: Azure Resource Graph (recommended)

ARG can query all capacity reservations across resource groups in a single call, filtering by location, VM size, and zone. This is the most efficient approach.

⚠️ Prerequisite: az extension add --name resource-graph

You must collapse this query to a single line before running it:

az graph query -q "
  Resources
  | where type =~ 'Microsoft.Compute/capacityReservationGroups/capacityReservations'
  | where location =~ '<region>'
  | where properties.provisioningState =~ 'Succeeded'
  | where sku.name =~ '<vm-size>'
  | project id,
            crgId = extract('(.*)/capacityReservations', 1, id),
            resourceGroup,
            zones,
            size = sku.name,
            capacity = coalesce(sku.capacity, 0),
            associationCount = coalesce(array_length(properties.virtualMachinesAssociated), 0),
            location
" --query "data[]" -o table

The crgId in the output is the parent Capacity Reservation Group resource ID — this is the value to use when associating a VM or VMSS.

To further narrow results for zonal VMs, add a zone filter:

| where zones has '<zone>'

Option 2: CLI enumeration

If ARG is unavailable, list CRGs per resource group and inspect their reservations:

# List all CRGs
az capacity reservation group list -o table

# List reservations within a CRG and check for matching size/capacity
az capacity reservation list \
  -g <rg> \
  --capacity-reservation-group <crg-name> \
  --query "[?sku.name=='<vm-size>'].{name:name, size:sku.name, capacity:sku.capacity, zones:zones}" \
  -o table

Estimating Reservation Cost

Capacity reservations are billed at the same pay-as-you-go rate as the underlying VM size, whether or not VMs are running against them. Use the Retail Prices API guide (unauthenticated) to look up hourly rates.

Estimated monthly cost: quantity × hourly rate × 730

⚠️ Prices returned are estimates based on current retail pay-as-you-go rates, not a final cost or contractual commitment. Actual charges may vary due to taxes, discounts (Reserved Instances, Savings Plans), or price changes.

Important Notes

• Deletion is blocked until prerequisites are met: Azure rejects a CRG delete unless all VMs/VMSS are disassociated and all capacity reservations are deleted. Order: disassociate VMs/VMSS → delete reservations → delete group.
• Quota required: Capacity reservations consume vCPU quota just like running VMs.

Learn More

• Azure Capacity Reservations documentation
• Create a Capacity Reservation
• Association and disassociation