Resizing a Server

Last changed: 2025-03-14

It is possible to resize a server (instance) by changing to a different flavor. This has some caveats and pitfalls, however. Be sure to have a backup of important data in case it goes wrong!

Caveats and Pitfalls

Resizing can sometimes be unpredictable, and worst case is that the instance is destroyed and unrecoverable. Follow these simple policies for best results:

1. Only within the same flavor class

   You can resize between flavors in the same class of flavors, e.g. between m1, c1 and d1 flavors. Examples:

   • m1.small → m1.large

   • m1.small → d1.small

   • m1.medium → c1.medium

   • shpc.m1a.2xlarge → shpc.c1a.4xlarge

   • shpc.m1a.2xlarge → shpc.m1ad1.2xlarge

   You can not resize between e.g. m1 and shpc.m1a.

2. The disk of the new flavor must be same size or larger

   An attempt to resize into a flavor with a smaller disk size will fail. The instance will be fine, but resizing will simply fail.

3. Do not resize vGPU instances

   Due to the nature of vGPU these instances can not be resized. Your only option is to delete the existing vGPU instance and create a new with a different flavor.

4. Do not leave the instance in VERIFY_RESIZE state

   The resize process involves two steps, where the last step is to confirm or revert the resize. Instances that are being resized and not yet confirmed or reverted should not be used in any form of production. They will also interfere with NREC maintenance as they cannot be migrated while in this state.

How to Resize

The example shows how to resize from m1.small to m1.large. This will be fine as both flavors are in the m1 flavor set, and we’re resizing to a larger disk (10GB → 20GB).

Via NREC Dashboard

1. Navigate to Compute → Instances:

   

2. In the drop-down menu, select Resize Instance:

   

3. In the pop-up window, select m1.large as the new flavor and click Resize:

   

   The system will now use the original instance as an image when creating a new instance using the new flavor, while backing up the original instance.

4. You now have the option to either confirm or revert the resize operation. Log into the instance, check that it works. You should be able to confirm that it is using the larger flavor.

   If you want to confirm the resize, select Confirm Resize/Migrate:

   

   If you want to revert the resize, select Revert Resize/Migrate in the drop-down menu:

   

5. If you opted to confirm the resize, the instance is now resized:

   

Via OpenStack CLI

The procedure is the same with OpenStack CLI:

1. We start with an instance of flavor m1.small:

   $ openstack server list
   +--------------------------------------+-------------+--------+----------------------------------------+-------------------+----------+
   | ID                                   | Name        | Status | Networks                               | Image             | Flavor   |
   +--------------------------------------+-------------+--------+----------------------------------------+-------------------+----------+
   | 12fe44f6-b9ca-4317-9626-9492a6d348f2 | resize-test | ACTIVE | IPv6=10.2.3.166, 2001:700:2:8201::1010 | GOLD Alma Linux 9 | m1.small |
   +--------------------------------------+-------------+--------+----------------------------------------+-------------------+----------+
   

2. Initiate the resize:

   $ openstack server resize --flavor m1.large 12fe44f6-b9ca-4317-9626-9492a6d348f2
   

3. After a few moments, the server should be in status VERIFY_RESIZE:

   $ openstack server show 12fe44f6-b9ca-4317-9626-9492a6d348f2 -c status
   +-----------+---------------+
   | Field     | Value         |
   +-----------+---------------+
   | status    | VERIFY_RESIZE |
   +-----------+---------------+
   

4. You now have the option to either confirm or revert the resize operation. Log into the instance, check that it works. You should be able to confirm that it is using the larger flavor.

   If you want to confirm the resize, run:

   $ openstack server resize confirm 12fe44f6-b9ca-4317-9626-9492a6d348f2
   

   If you want to revert the resize, run:

   $ openstack server resize revert 12fe44f6-b9ca-4317-9626-9492a6d348f2
   

5. If you opted to confirm the resize, the instance is now resized:

   $ openstack server list
   +--------------------------------------+-------------+--------+----------------------------------------+-------------------+----------+
   | ID                                   | Name        | Status | Networks                               | Image             | Flavor   |
   +--------------------------------------+-------------+--------+----------------------------------------+-------------------+----------+
   | 12fe44f6-b9ca-4317-9626-9492a6d348f2 | resize-test | ACTIVE | IPv6=10.2.3.166, 2001:700:2:8201::1010 | GOLD Alma Linux 9 | m1.large |
   +--------------------------------------+-------------+--------+----------------------------------------+-------------------+----------+