RFC: Add release policy

doc/development/rfc/release_policy.md

@@ -0,0 +1,122 @@
+# RFC: Release Policy
+
+Author: Vaclav Petras
+
+Status: Draft
+
+## Goal
+
+The goal of this document is to define when releases should be created
+and what types of releases should be created.
+
+## Summary
+
+One major or minor release should be released per year.
+This becomes the only actively maintained release series
+which is subsequently updated by micro releases as needed.
+Individual contributors can step up to maintain an older release series.
+
+## Types of Releases
+
+We recognize major, minor, micro releases and additional helper versions
+each with its unique purpose.
+
+The releases follow rules and numbering specified in the Version Numbering RFC.
+
+### Major and Minor
+
+Both major and minor releases bring new features to the users
+and in that regard should receive similar attention by the contributors.
+However, they differ in how backwards compatibility is handled.
+
+While major release brings features just like a minor release,
+it may also bring changes breaking backwards compatibility
+such as breaking API changes. Additionally, contributors may decide
+to include certain feature into a major release rather than a minor release
+if the feature has a potential to negatively impact some users or use cases.
+A major release may include a particularly important feature or a set of
+features, but that's not required. The purpose of a major release is to bring
+changes which cannot be included into a minor release such as
+backwards-incompatible changes in API or unusually large code rewrites.
+It may or may not be used to bring revolutionary changes or highlight specific
+features.
+
+Minor release may bring any new features, small or big, as long as backwards
+compatibility is kept, e.g., an automated procedure relying on public API
+still works. The purpose of a minor release is to bring features to the users
+as soon as possible with software stability and compatibility, but without
+a need to wait for a major release.
+
+Both major and minor releases may include bugfixes which may or may not be
+already included in a micro release of the previous major or minor release.
+
+A special effort is put into keeping backwards compatibility.
+While this is a requirement for minor versions, the community makes extra effort
+even for major releases to maximize backwards compatibility so that users can
+conveniently transition to new versions. This is, however, not guaranteed and
+it depends on many factors.
+
+### Micro
+
+Micro releases should contain only bugfixes.
+Their purpose is to fix issues with a particular major or minor release.
+They provide software stability and fixes to the users.
+
+A minor release should be considered instead of a micro release when
+a bugfix is large, a bugfix has unclear side-effects, or it is not clear
+whether a particular change is bugfix or a feature given that, in practice,
+the line between a bugfix and a feature is not completely clear.
+
+### Pre-releases and Daily Builds
+
+There can be zero or more release candidates, i.e., pre-releases,
+for each major, minor, or micro release. The specifics are determined
+by the Release Procedure RFC.
+
+There can be daily or per-commit frequent builds 
+which can serve as preview versions or versions for testing.
+Other frequencies are permitted but not recommended.
+
+### Post-releases and Build Versions
+
+There can be subsequent builds of a specific release
+if build or packaging process failed and needs fixing.
+However, there shouldn't be any post-releases, i.e.,
+if there is a change in the code base to fix a flaw in a release,
+a new micro release should be created.
+
+## Frequency
+
+One major or minor release should be released at least once a year.
+More than one major or minor release may be released
+if the contributors consider that necessary or advantageous.
+There is no frequency requirement for major releases, but
+the practice and rhythm so far was to release a new major version
+before the minor version number reaches the value ten which translates
+to a major release every five to ten years.
+
+There can be zero or more micro releases per year for different major or minor
+releases based on the needs of the community and practically driven by the number
+of fixes accumulated.
+
+## Maintenance
+
+At any time there is one actively updated, maintained, and supported release series
+which is started by a release of a new major or minor version.
+There are micro versions releases in this series throughout the year as needed.
+
+Once a new major or minor version is released, the old release series goes to
+a low maintenance mode and no further releases are planned.
+However, any low maintenance series can be updated on demand.
+If a contributor submits a patch to fix a bug, it will be likely accepted and
+a new release will be created when there are enough changes accumulated.
+Alternatively the contributor might receive support in creating the release as
+a temporary release manager.
+Security fixes will be given special consideration in light of how wide
+the usage of a particular release series is.
+
+## Relation to Other Documents
+
+* Release procedure covers branching and creation of pre-releases.
+* Version number covers how major, minor, micro releases are numbered
+  and what types of changes can be included in a release.