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 + zone

Associating 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>   # optional

Option 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 None

Option 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

Learn More

• Associate a VM to a Capacity Reservation Group
• Remove/disassociate a VM from a Capacity Reservation Group
• Remove/disassociate a VMSS from a Capacity Reservation Group