CloudStack KVM Host Reinstallation – Reusing Hostname and IP

[shakibshalim74]

Hello CloudStack Community,

We are currently running Apache CloudStack 4.19.3 with KVM hosts on Ubuntu 20.04. Before upgrading CloudStack to 4.22, we plan to upgrade the KVM hypervisors to Ubuntu 24.04 LTS.

For example, we have a KVM host cshost10.xyz.com with IP 10.1.1.10. We plan to reinstall the OS with Ubuntu 24.04 and then reinstall/configure the CloudStack agent, libvirt, and required packages.

Our question is: Can we safely reuse the same hostname and IP (cshost10.xyz.com / 10.1.1.10) after the fresh OS installation and reconnect it to the existing CloudStack host record, without modifying or manually changing the CloudStack database?

Or is it recommended to use a new hostname/IP and add it as a new host?

Any guidance or recommended best practices would be appreciated.

Regards,
Shakib

[akaydinb]

Hi Shakib,
I have tested a quite similar case in our test environment. We're running Apache Cloudstack v4.20.1.0 with KVM hosts on Ubuntu 24.04. I've put a host into maintenance and backed up /etc/cloudstack/agent/agent.properties, SSH keys of root (i.e. /root/.ssh/id_rsa.pub.cloud and /root/.ssh/id_rsa.cloud), as well as host keys pairs under /etc/ssh. Then I wiped the server completely, installed Ubuntu 26.04 from scratch with same IP, same hostname etc. and configured it for Cloudstack. I finally restored above mentioned files and restarted cloudstack-agent service. After these steps, the connection between the host and Cloudstack Manager was successful, the server appeared online and I was able to disable maintenance mode on the host, with a minor issue: Since I forgot to backup client certificates (/etc/cloudstack/agent/cloud.key, /etc/cloudstack/agent/cloud.crt) and listen_tls` setting in libvirtd.conf is default zero, the server appeared as "Unsecure". For this, I simply clicked to "Provision host security keys", et voilà. Everything was back online like before.

I strongly believe, that backing up ssh keys shouldn't be actually necessary, yet agent.properties is definitely necessary. And the certificates are up to you.

Caution: I did this only in a test environment and have not tested throughly. Use this at your own risk for unforeseen problems.