Ubuntu Pro Client feature deprecation policy

When the Pro Client introduces new features, particularly features designed for other software to integrate with, we assume those features become relied-upon in all Ubuntu releases we support. That includes the oldest and also the newest (at time of writing, the oldest is 16.04 and the newest is 24.04). The newest supported Ubuntu release typically has ~12 years of life left between LTS, ESM and Legacy coverage. That means we need to support any given feature in a backwards compatible-way for at least 12 years. This is particularly true for any integration point with machine-readable output (e.g. our API functions, any command with JSON-formatted output). It is also true for important features that, even if lacking intentional machine-usability, are likely to be used in automation (e.g. any form of pro attach or pro enable that doesn’t require interaction).

Removing features by release

We maintain the LTS promise of stability for every supported LTS. Therefore, we cannot remove a given feature from any LTS that already has the feature. Instead, we will remove features starting on a devel Ubuntu release onward. To make the transition more apparent to users and give them time to adjust, we will only remove features in interim devel releases. We will not remove a feature for the first time in an LTS devel release. When the given feature is invoked on a release where it has been removed, the Pro Client will return an error code and message describing what to do instead of using the removed feature.

Features will only be per-release-removed once a better replacement is available on all supported Ubuntu releases via Stable Release Update (SRU). The soonest allowed per-release-removal is the next new interim release after the replacement is SRU’d to all Ubuntu releases.

Deprecation warnings on releases that keep the feature

When a feature is removed in e.g. 24.10 onward, it will continue to exist in all prior supported releases; however, features in pro are often expected to work consistently across all supported Ubuntu releases. Any feature we remove should either not apply to new Ubuntu releases, or should have a better alternative available that does work consistently across all supported Ubuntu releases. So when we remove a feature in future releases, all releases that still support the feature should start showing a deprecation warning. This warning will tell the user that this feature will not work on future Ubuntu releases, and point them to the alternative.

Documentation

For features that are removed per-release, we will add notices to the related documentation noting which Ubuntu releases they are supported on, and also directing the reader to the replacement.