Associating and Disassociating VMs/VMSS with a Capacity Reservation Group
Association Model
Capacity Reservation Group (CRG)
├── Capacity Reservation: Standard_D4s_v5 × 5 (Zone 1)
├── Capacity Reservation: Standard_D4s_v5 × 3 (Zone 2)
└── Capacity Reservation: Standard_E8s_v5 × 2 (Zone 1)
VM / VMSS
└── capacityReservationGroup.id = <CRG resource ID>
└── Azure auto-matches to a reservation with the right VM size + zoneAssociating VMs
Set the capacityReservationGroup property when creating or updating a VM.
New VM
az vm create \
-g <rg> \
-n <vm-name> \
--image <image> \
--size Standard_D4s_v5 \
--zone 1 \
--capacity-reservation-group <crg-id>Existing VM
Zonal VMs can be associated while running:
az vm update -g <rg> -n <vm-name> --capacity-reservation-group <crg-id>Regional VMs (no zone) must be deallocated first:
az vm deallocate -g <rg> -n <vm-name>
az vm update -g <rg> -n <vm-name> --capacity-reservation-group <crg-id>
az vm start -g <rg> -n <vm-name>Associating VMSS
az vmss create \
-g <rg> \
-n <vmss-name> \
--image <image> \
--vm-sku Standard_D4s_v5 \
--instance-count 5 \
--zones 1 \
--capacity-reservation-group <crg-id>Existing VMSS can be associated using az vmss update similarly to VMs. Regional VMSS must be deallocated first. Zonal VMSS can be associated without deallocating, but this is currently a Preview feature.
Disassociating from a Capacity Reservation Group
Both the VM/VMSS and the underlying capacity reservation logically occupy capacity. Azure imposes constraints to avoid ambiguous allocation states, so you cannot simply remove the association while resources are running against it.
There are three ways to disassociate. The commands below use az vm — for VMSS, substitute az vmss and add az vmss update-instances --instance-ids "*" as a final step when using a Manual upgrade policy.
Option 1: Deallocate, then remove association
Best when the VM/VMSS can tolerate downtime.
az vm deallocate -g <rg> -n <vm-name>
az vm update -g <rg> -n <vm-name> --capacity-reservation-group None
az vm start -g <rg> -n <vm-name> # optionalOption 2: Set reserved quantity to zero, then remove association
Best when the VM/VMSS cannot be deallocated and the reservation is no longer needed.
az capacity reservation update \
-g <rg> --capacity-reservation-group <crg> \
-n <reservation-name> --capacity 0
az vm update -g <rg> -n <vm-name> --capacity-reservation-group NoneOption 3: Delete the VM/VMSS
Deleting the resource automatically removes the association. Some latency may occur before the capacity reservation allocation state updates.
VMSS Upgrade Policy Behavior
| Policy | Behavior |
|---|---|
| Automatic | Instances update automatically — no further action needed |
| Rolling | Instances update in batches with an optional pause between them |
| Manual | You must run az vmss update-instances --instance-ids "*" per update |