Software upgrades
The Ubuntu OpenStack team maintains the Ceph charms. Before upgrading do check their project’s latest Release Notes for any possible messaging with respect to the Ceph charms as well as the Upgrade notes appendix in this guide.
There are three pieces of software in a Charmed Ceph deployment that can be upgraded:
- charms
- cluster node operating system
- Ceph itself
Providing the cluster is designed to withstand a cluster node going offline (a necessity for upgrading a node’s OS) and still able to service its regular workload, a Charmed Ceph cluster can be upgraded with zero downtime.
The upgrade process for Charmed OpenStack, which includes Ceph, is covered in the OpenStack Charms Deployment Guide under Series upgrade and OpenStack upgrades. It is recommended to read these documents before upgrading your Ceph cluster.
Looking at this in terms of upgrade scenarios helps to clarify the required steps. The previous graphic is also very useful in this context:
Scenarios
#1 - A specific Ubuntu release is desired
Current state:
- Ubuntu 18.04 LTS
- UCA bionic-train
- Ceph Nautilus
Goal state: Ubuntu 20.04 LTS
Upgrade path:
- charms to latest stable revision
- UCA to bionic-ussuri
- Ubuntu to 20.04 LTS
Final result: Ceph Octopus on Ubuntu 20.04 LTS nodes
#2 - A specific Ceph release is desired
Current state:
- Ubuntu 16.04 LTS
- UCA xenial-queens
- Ceph Luminous
Goal state: Ceph Nautilus
Upgrade path:
- charms to latest stable revision
- Ubuntu to 18.04 LTS
- UCA to bionic-rocky
- UCA to bionic-stein
- UCA to bionic-train
Final result: Ceph Nautilus on Ubuntu 18.04 LTS nodes
The next three sections will go into detail on how to complete each respective upgrade type.