2.8. Planning for a Compute node upgrade
After you upgrade your Compute nodes from Red Hat OpenStack Platform (RHOSP) 16.2 to RHOSP 17.1, you can choose one of the following options to upgrade the Compute host operating system:
- Keep a portion of your Compute nodes on Red Hat Enterprise Linux (RHEL) 8.4, and upgrade the rest to RHEL 9.2. This is referred to as a Multi-RHEL environment.
- Upgrade all Compute nodes to RHEL 9.2, and complete the upgrade of the environment.
- Keep all Compute nodes on RHEL 8.4. The lifecycle of RHEL 8.4 applies.
Benefits of a Multi-RHEL environment
You must upgrade all of your Compute nodes to RHEL 9.2 to take advantage of any hardware-related features that are only supported in RHOSP 17.1, such as vTPM and Secure Boot. However, you might require that some or all of your Compute nodes remain on RHEL 8.4. For example, if you certified an application for RHEL 8, you can keep your Compute nodes running on RHEL 8.4 to support the application without blocking the entire upgrade.
The option to upgrade part of your Compute nodes to RHEL 9.2 gives you more control over your upgrade process. You can prioritize upgrading the RHOSP environment within a planned maintenance window and defer the operating system upgrade to another time. Less downtime is required, which minimizes the impact to end users.
If you plan to upgrade from RHOSP 17.1 to RHOSP 18.0, you must upgrade all hosts to RHEL 9.2. If you continue to run RHEL 8.4 on your hosts beyond the Extended Life Cycle Support phase, you must obtain a TUS subscription.
Limitations of a Multi-RHEL environment
The following limitations apply in a Multi-RHEL environment:
- Compute nodes running RHEL 8 cannot consume NVMe-over-TCP Cinder volumes.
- You cannot use different paths for socket files on RHOSP 16.2 and 17.1 for collectd monitoring.
- You cannot mix ML2/OVN and ML2/OVS mechanism drivers. For example, if your RHOSP 16.2 deployment included ML2/OVN, your Multi-RHEL environment must use ML2/OVN.
- FIPS is not supported in a Multi-RHEL environment. FIPs deployment is a Day 1 operation. FIPS is not supported in RHOSP 16.2. As a result, when you upgrade from RHOSP 16.2 to 17.1, the 17.1 environment does not include FIPS.
- Instance HA is not supported in a Multi-RHEL environment.
- Edge topologies are currently not supported.
- If you are upgrading to RHOSP 17.1.3 or earlier, before you start the system upgrade, you must clear the workloads from each Compute host that you plan to upgrade. Any workloads that are running go into an error state. To avoid this issue, either live migrate your workloads from the Compute host to another host, or shut the workloads down. For more information about live migration, see Live migrating an instance in Configuring the Compute service for instance creation.
All HCI nodes in supported Hyperconverged Infrastructure environments must use the same version of Red Hat Enterprise Linux as the version used by the Red Hat OpenStack Platform controllers. If you wish to use multiple Red Hat Enterprise versions in a hybrid state on HCI nodes in the same Hyperconverged Infrastructure environment, contact the Red Hat Customer Experience and Engagement team to discuss a support exception.
Upgrading Compute nodes
Use one of the following options to upgrade your Compute nodes:
- To perform a Multi-RHEL upgrade of your Compute nodes, see Upgrading Compute nodes to a Multi-RHEL environment.
- To upgrade all Compute nodes to RHEL 9.2, see Upgrading Compute nodes to RHEL 9.2.
- If you are keeping all of your Compute nodes on RHEL 8.4, no additional configuration is required.
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