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In OpenShift Container Platform 4.1, Red Hat introduced the concept of channels for recommending the appropriate release versions for cluster upgrades. By controlling the pace of upgrades, these upgrade channels allow you to choose an upgrade strategy. Upgrade channels are tied to a minor version of OpenShift Container Platform. For instance, OpenShift Container Platform 4.8 upgrade channels recommend upgrades to 4.8 and upgrades within 4.8. They also recommend upgrades within 4.7 and from 4.7 to 4.8, to allow clusters on 4.7 to eventually upgrade to 4.8. They do not recommend upgrades to 4.9 or later releases. This strategy ensures that administrators explicitly decide to upgrade to the next minor version of OpenShift Container Platform.

Upgrade channels control only release selection and do not impact the version of the cluster that you install; the openshift-install binary file for a specific version of OpenShift Container Platform always installs that version.

OpenShift Container Platform 4.8 offers the following upgrade channels:

  • candidate-4.8

  • fast-4.8

  • stable-4.8

  • eus-4.y (only when running an even-numbered 4.y cluster release, like 4.8)

If you do not want the Cluster Version Operator to fetch available updates from the upgrade recommendation service, you can use the oc adm upgrade channel command in the OpenShift CLI to configure an empty channel. This configuration can be helpful if, for example, a cluster has restricted network access and there is no local, reachable upgrade recommendation service.

Red Hat recommends upgrading to versions suggested by Openshift Update Service only. For minor version upgrade, versions must be contiguous. Red Hat does not test upgrades to noncontiguous versions and cannot guarantee compatibility with earlier versions.

Upgrade channels and release paths

Cluster administrators can configure the upgrade channel from the web console.

candidate-4.8 channel

The candidate-4.8 channel contains candidate builds for a z-stream (4.8.z) and previous minor version releases. Release candidates contain all the features of the product but are not supported. Use release candidate versions to test feature acceptance and assist in qualifying the next version of OpenShift Container Platform. A release candidate is any build that is available in the candidate channel, including ones that do not contain a pre-release version such as -rc in their names. After a version is available in the candidate channel, it goes through more quality checks. If it meets the quality standard, it is promoted to the fast-4.8 or stable-4.8 channels. Because of this strategy, if a specific release is available in both the candidate-4.8 channel and in the fast-4.8 or stable-4.8 channels, it is a Red Hat-supported version. The candidate-4.8 channel can include release versions from which there are no recommended updates in any channel.

You can use the candidate-4.8 channel to upgrade from a previous minor version of OpenShift Container Platform.

Release candidates differ from the nightly builds. Nightly builds are available for early access to features, but updating to or from nightly builds is neither recommended nor supported. Nightly builds are not available in any upgrade channel. You can reference the OpenShift Container Platform release statuses for more build information.

fast-4.8 channel

The fast-4.8 channel is updated with new and previous minor versions of 4.8 as soon as Red Hat declares the given version as a general availability release. As such, these releases are fully supported, are production quality, and have performed well while available as a release candidate in the candidate-4.8 channel from where they were promoted. Some time after a release appears in the fast-4.8 channel, it is added to the stable-4.8 channel. Releases never appear in the stable-4.8 channel before they appear in the fast-4.8 channel.

You can use the fast-4.8 channel to upgrade from a previous minor version of OpenShift Container Platform.

stable-4.8 channel

While the fast-4.8 channel contains releases as soon as their errata are published, releases are added to the stable-4.8 channel after a delay. During this delay, data is collected from Red Hat SRE teams, Red Hat support services, and pre-production and production environments that participate in connected customer program about the stability of the release.

You can use the stable-4.8 channel to upgrade from a previous minor version of OpenShift Container Platform.

eus-4.y channel

In addition to the stable channel, all even-numbered minor versions of OpenShift Container Platform offer an Extended Update Support (EUS). These EUS versions extend the Full and Maintenance support phases for customers with Standard and Premium Subscriptions to 18 months.

Although there is no difference between stable-4.y and eus-4.y channels until OpenShift Container Platform 4.y transitions to the EUS phase, you can switch to the eus-4.y channel as soon as it becomes available.

When upgrades to the next EUS channel are offered, you can switch to the next EUS channel and upgrade until you have reached the next EUS version.

This upgrade process does not apply for upgrades coming from the eus-4.6 channel. Upgrading to the next EUS channel from eus-4.6 requires a serial set of version upgrades, from 4.6 to 4.7 to 4.8.

Upgrade version paths

OpenShift Container Platform maintains an upgrade recommendation service that understands the version of OpenShift Container Platform 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 fast-4.8 channel:

  • 4.8.0

  • 4.8.1

  • 4.8.3

  • 4.8.4

The service recommends only upgrades that have been tested and have no serious issues. It will not suggest updating to a version of OpenShift Container Platform that contains known vulnerabilities. For example, if your cluster is on 4.8.1 and OpenShift Container Platform suggests 4.8.4, then it is safe for you to update from 4.8.1 to 4.8.4. Do not rely on consecutive patch numbers. In this example, 4.8.2 is not and never was available in the channel.

Update stability depends on your channel. The presence of an update recommendation in the candidate-4.8 channel does not imply that the update is supported. It means that no serious issues have been found with the update yet, but there might not be significant traffic through the update to suggest stability. The presence of an update recommendation in the fast-4.8 or stable-4.8 channels at any point is a declaration that the update is supported. While releases will never be removed from a channel, update recommendations that exhibit serious issues will be removed from all channels. Updates initiated after the update recommendation has been removed are still supported.

Red Hat will eventually provide supported update paths from any supported release in the fast-4.8 or stable-4.8 channels to the latest release in 4.8.z, although there can be delays while safe paths away from troubled releases are constructed and verified.

Fast and stable channel use and strategies

The fast-4.8 and stable-4.8 channels present a choice between receiving general availability releases as soon as they are available or allowing Red Hat to control the rollout of those updates. If issues are detected during rollout or at a later time, upgrades to that version might be blocked in both the fast-4.8 and stable-4.8 channels, and a new version might be introduced that becomes the new preferred upgrade target.

Customers can improve this process by configuring pre-production systems on the fast-4.8 channel, configuring production systems on the stable-4.8 channel, and participating in the Red Hat connected customer program. Red Hat uses this program to observe the impact of updates on your specific hardware and software configurations. Future releases might improve or alter the pace at which updates move from the fast-4.8 to the stable-4.8 channel.

Restricted network clusters

If you manage the container images for your OpenShift Container Platform clusters yourself, you must consult the Red Hat errata that is associated with product releases and note any comments that impact upgrades. During upgrade, the user interface might warn you about switching between these versions, so you must ensure that you selected an appropriate version before you bypass those warnings.

Switching between channels

A channel can be switched from the web console or through the patch command:

$ oc patch clusterversion version --type json -p '[{"op": "add", "path": "/spec/channel", "value": "<channel>”}]'

The web console will display an alert if you switch to a channel that does not include the current release. The web console does not recommend any updates while on a channel without the current release. You can return to the original channel at any point, however.

Changing your channel might impact the supportability of your cluster. The following conditions might apply:

  • Your cluster is still supported if you change from the stable-4.8 channel to the fast-4.8 channel.

  • You can switch to the candidate-4.8 channel but, some releases for this channel might be unsupported.

  • You can switch from the candidate-4.8 channel to the fast-4.8 channel if your current release is a general availability release.

  • You can always switch from the fast-4.8 channel to the stable-4.8 channel. There is a possible delay of up to a day for the release to be promoted to stable-4.8 if the current release was recently promoted.