Openstack resize instance no valid host was found

 Today I had to resize an instance in my OpenStack and noticed that I couldn’t do that because of an error: “No valid host was found. No valid host found for resize (HTTP 400)“. Soon enough I understood OpenStack was trying to resize the instance by using another host, however my setup is a all-in-one node.

The solution

is rather simple: set the property allow_resize_to_same_host to true in /etc/nova/nova.conf . After this restart nova-compute and nova-api by doing

# systemctl restart openstack-nova-compute

# systemctl restart openstack-nova-api

Also be careful, if you set up to save the root disk inside of Cinder (boot and create volume). I still haven’t found a way to resize using Nova. Inexplicably the request times out and the instance enters the state VM_ERROR. The workaround I used is:

1. Delete the instance while keeping the volume that contains the root.
2. Create a new instance booting from the root volume of the precedent.
3. Re-assign floating IP.

EDIT: After a few tweaks and a reboot I can now resize instances with root disk inside Cinder. It was probably due to a malfunction in the cinder-scheduler component.