# Revision history [back]

### Is it possible to upgrade nova-compute first?

Hello,

In our environment we still have everywhere OpenStack Train and now trying to upgrade to Ussuri release. We want to start with physical servers first so that we can test whatever is running on VMs first, before upgrading OpenStack control plane.

However, it seems that it is not really possible. I've set compute=train for [upgrade_levels] both on VM that hosts nova services (API, placement, etc.) and on server where I'm trying to use Ussuri.

During the deployment of the VM I see:

 2020-08-24 21:33:22.112 9849 ERROR oslo_messaging.rpc.server IncompatibleObjectVersion: Version 1.4 of InstanceActionEvent is not supported, supported version is 1.3 

Does it mean that I simply should update openstack service nodes first and only after that servers or I miss some setting in configuration or it is a bug?