In OpenShift Container Platform (OCP) 4.1 Red Hat introduced the concept of upgrade channels for recommending the appropriate upgrade versions to your cluster. Upgrade channels separate upgrade strategies and also are used to control the cadence of updates. Channels are tied to a minor version of OpenShift (for instance, 4.2 channels will never include an upgrade to a 4.3 release) to ensure administrators must make an explicit decision to upgrade to the next minor version of OpenShift. Channels only control updates and have no impact on the version of the cluster you install - the openshift-install binary for a given patch level of OpenShift always installs that patch level.
OCP 4.1 included two upgrade channels:
Updates from previous 4.1 versions were first delivered to prerelease-4.1 and then became available in the stable-4.1 channel after a short delay to monitor for any issues encountered during upgrades.
OCP 4.2, which includes the upgrade from the previous 4.1 release, has three upgrade channels to choose from:
The upgrade channels contain two types of updates:
General Availability Software (or GA): These versions of OpenShift are fully supported and are considered production quality. You may upgrade to the general availability release from either of the fast and stable channels
Release Candidate Software (or RC): These versions of OpenShift are representative of the eventual general availability release and are available only in the candidate-4.2 channel. The release candidate will contain all the features of the product. You are allowed to upgrade from a release candidate to another release candidate and to upgrade from a previous minor version of OpenShift to the current release candidate. Release candidate builds are not supported by Red Hat and you will not be able to upgrade from a release candidate to the general availability release of OpenShift. Candidates should be used to test feature acceptance and assist in qualifying the next version of OpenShift in your infrastructure.
- Note: Release candidates differ from the nightly builds found on try.openshift.com. You cannot upgrade nightly builds to nightly builds. Nightly builds are available for early access to features but are not upgradable or supported.
For GA versions, the fast and stable channels present a choice between receiving updates as soon as they are available or allowing Red Hat to control the rollout of those updates.
The fast channel is updated with new 4.2 patch versions as soon as Red Hat declares they are generally available. Use this channel if you wish to receive updates as soon as they are available or for your pre-production environments when participating in the connected customer program. This channel will contain all z-stream (4.2.z) updates but will not suggest upgrades to the next minor release (4.3.z) when the next minor release is available.
The stable channel will contain updates on a time delay as they are gradually rolled out to customers based on data from our SRE teams, support services, and pre-production and production environments that participate in our connected customer program, rather than being immediately available as they are in the fast channel. For patch and CVE fixes this can range from several hours to a day and allows an extra period of assessment in how the software performs. If issues are detected during rollout, upgrades to that version may be blocked in both the fast and stable channels, and a new version may be introduced that will be the new preferred upgrade target.
Customers can improve this process by configuring pre-production systems on the fast channel, production systems on the stable channel, and participating in the Red Hat’s connected customer program - this allows Red Hat to observe the impact of updates on your specific hardware and software configurations. Future releases may improve or alter the pace at which updates move from the fast to the stable channels.
If issues are discovered with an upgrade between patch levels, Red Hat may withdraw that suggested upgrade for affected versions. A newer patch would become available in the appropriate channels and be suggested for upgrade.
Upgrade Version Paths
OpenShift maintains an upgrade recommendation service that understands the version of OpenShift you have installed as well as the path to take within the channel you choose to get you to the next release. You can imagine seeing the following in the the fast-4.2 channel:
The service only recommends upgrades that have been tested and have no known issues. If you are on 4.2.1 and OpenShift is allowing you to select 4.2.4, then it is safe for you to go from 4.2.1 to 4.2.4. Likewise, the absence of 4.2.2 may be due to a CVE that was fixed in 4.2.3 and Red Hat no longer suggests upgrading to a known vulnerable version. If an issue is found that results in a new version being retracted from the recommendations, Red Hat will release a new version that is capable of upgrading from all necessary versions, including the retracted version.
Customers which have chosen to not be connected to Red Hat and are curating their own OpenShift container image content manually should consult the Red Hat errata associated with product releases and note any comments impacting upgrades. During upgrade the user interface may caution about switching between these versions and it is up to the customer to ensure they have correctly selected the appropriate version before bypassing those cautions.
Switching Between Channels
It is supported for customers to switch between the fast and stable channel at any time. Channels only offer suggested
upgrades, and will never suggest a dangerous upgrade. If you switch to the candidate channel after installing from a GA version, you will see a warning the current version is not recognized, and you can safely switch back to a GA channel.