Comment 0 for bug 1843708

Description
===========

When we want to rebuild an instance and change the keypair we can specified it with :
openstack --os-compute-api-version 2.54 server rebuild --image "Debian 10" --key-name key1 instance1

This comes from this implementation :
https://review.opendev.org/#/c/379128/
https://specs.openstack.org/openstack/nova-specs/specs/queens/implemented/rebuild-keypair-reset.html

But when rebuilding the instance, Cloud-Init will set the key in authorized_keys from
http://169.254.169.254/openstack/latest/meta_data.json

And this meta_data.json uses the keys from instance_extra tables
But the keypair will be updated in the 'instances' table but not in the 'instance_extra' table.

So the keypair is not updated inside the VM

May be this is the function for saving the keypair, but the save() do nothing :
https://opendev.org/openstack/nova/src/branch/master/nova/objects/instance.py#L714

Steps to reproduce
==================

- Deploy a DevStack
- Boot an instance with keypair key1
- Rebuild it with key2
- A nova show will show the key_name key2, keypairs object in table instance_extra is not updated and you cannot connect with key2 to the instance

Expected result
===============
Connecte to the Vm with the new keypair added during the rebuild call

Actual result
=============
The keypair added during the rebuild call is not set in the VM

Environment
===========
I tested it on a Devstack from master and we have the behaviour.
NOVA : commit 5fa49cd0b8b6015aa61b4312b2ce1ae780c42c64