Resize (or Server resize) is the ability to change the flavor of a server, thus allowing it to upscale or downscale according to user needs. For this feature to work properly, you might need to configure some underlying virt layers.
This document describes how to configure hosts for standard resize. For information on cross-cell resize <Cross-Cell Resize>, refer to /admin/configuration/cross-cell-resize.
This section needs to be updated for other virt drivers, shared storage considerations, etc.
Resize on KVM is implemented currently by transferring the images between compute nodes over ssh. For KVM you need hostnames to resolve properly and passwordless ssh access between your compute hosts. Direct access from one compute host to another is needed to copy the VM file across.
Cloud end users can find out how to resize a server by reading /user/resize.
There is a periodic task configured by configuration option :oslo.configresize_confirm_window (in seconds). If this value is not 0, the
nova-compute service will check whether servers are in a resized state longer than the value of :oslo.configresize_confirm_window and if so will automatically confirm the resize of the servers.