Can I resize a VM (add or remove resources like cores or memory)?

That is possible by changing the flavor of a VM.

Please keep in mind that VMs will be restarted during the resize process. You cannot resize a VM online.

Using the web interface (GUI):

  1. Change to the „Compute -> Instances“ overview page
  2. Click the down arrow in the Actions column of the VM you want to resize and click „Resize Instance“
  3. Select the new flavor you want to assign to this VM from the „New Flavor“ drop down list and click on „Resize“
  4. You will be returned to the Instances overview page with the VM in state „Resize/Migrate“
  5. Eventually it’s state wil change to „Confirm or Revert Resize/Migrate“. Click on the „Confirm Resize/Migrate“ button in the actions column of this VM.
  6. After a couple of moments it’s state will change to „Active“ and the newly resized VM will be booted and will allow you to log in.

Using the command line tools:

  1. openstack server resize –flavorThis command will attach the new flavor to the VM with the specified ID. Basically, it creates a new copy of the VM with the new flavor assigned. 2. 
    openstack server list

    Is needed to keep an eye on the VM’s status. The VM’s state will be RESIZE and eventually change to VERIFY_RESIZE. After the VM has entered this final state, you need to carry out one more command 3.

    openstack server resize --confirm

    This command confirms that the resized VM is in a working state. Thereafter the old VM will be deleted and you can use your newly resized one.