1# Associating and Disassociating VMs/VMSS with a Capacity Reservation Group
2 
3## Association Model
4 
5```text
6Capacity Reservation Group (CRG)
7├── Capacity Reservation: Standard_D4s_v5 × 5 (Zone 1)
8├── Capacity Reservation: Standard_D4s_v5 × 3 (Zone 2)
9└── Capacity Reservation: Standard_E8s_v5 × 2 (Zone 1)
10 
11VM / VMSS
12└── capacityReservationGroup.id = <CRG resource ID>
13    └── Azure auto-matches to a reservation with the right VM size + zone
14```
15 
16### Associating VMs
17 
18Set the `capacityReservationGroup` property when creating or updating a VM.
19 
20#### New VM
21 
22```bash
23az vm create \
24  -g <rg> \
25  -n <vm-name> \
26  --image <image> \
27  --size Standard_D4s_v5 \
28  --zone 1 \
29  --capacity-reservation-group <crg-id>
30```
31 
32#### Existing VM
33 
34Zonal VMs can be associated while running:
35 
36```bash
37az vm update -g <rg> -n <vm-name> --capacity-reservation-group <crg-id>
38```
39 
40Regional VMs (no zone) must be deallocated first:
41 
42```bash
43az vm deallocate -g <rg> -n <vm-name>
44az vm update -g <rg> -n <vm-name> --capacity-reservation-group <crg-id>
45az vm start -g <rg> -n <vm-name>
46```
47 
48### Associating VMSS
49 
50```bash
51az vmss create \
52  -g <rg> \
53  -n <vmss-name> \
54  --image <image> \
55  --vm-sku Standard_D4s_v5 \
56  --instance-count 5 \
57  --zones 1 \
58  --capacity-reservation-group <crg-id>
59```
60 
61Existing 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](https://learn.microsoft.com/en-us/azure/virtual-machines/capacity-reservation-associate-virtual-machine-scale-set).
62 
63## Disassociating from a Capacity Reservation Group
64 
65Both 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.
66 
67There 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.
68 
69### Option 1: Deallocate, then remove association
70 
71Best when the VM/VMSS can tolerate downtime.
72 
73```bash
74az vm deallocate -g <rg> -n <vm-name>
75az vm update -g <rg> -n <vm-name> --capacity-reservation-group None
76az vm start -g <rg> -n <vm-name>   # optional
77```
78 
79### Option 2: Set reserved quantity to zero, then remove association
80 
81Best when the VM/VMSS cannot be deallocated and the reservation is no longer needed.
82 
83```bash
84az capacity reservation update \
85  -g <rg> --capacity-reservation-group <crg> \
86  -n <reservation-name> --capacity 0
87az vm update -g <rg> -n <vm-name> --capacity-reservation-group None
88```
89 
90### Option 3: Delete the VM/VMSS
91 
92Deleting the resource automatically removes the association. Some latency may occur before the capacity reservation allocation state updates.
93 
94### VMSS Upgrade Policy Behavior
95 
96| Policy        | Behavior                                                               |
97|---------------|------------------------------------------------------------------------|
98| **Automatic** | Instances update automatically — no further action needed              |
99| **Rolling**   | Instances update in batches with an optional pause between them        |
100| **Manual**    | You must run `az vmss update-instances --instance-ids "*"` per update  |
101 
102## Learn More
103 
104- [Associate a VM to a Capacity Reservation Group](https://learn.microsoft.com/en-us/azure/virtual-machines/capacity-reservation-associate-vm)
105- [Remove/disassociate a VM from a Capacity Reservation Group](https://learn.microsoft.com/en-us/azure/virtual-machines/capacity-reservation-remove-vm)
106- [Remove/disassociate a VMSS from a Capacity Reservation Group](https://learn.microsoft.com/en-us/azure/virtual-machines/capacity-reservation-remove-virtual-machine-scale-set)
107