Re: RFC: LTS and stable release scheme

[George Dunlap <george.dunlap@citrix.com>]

On 06/10/15 12:07, Wei Liu wrote:
> Hi all
> 
> A majority of developers express interests in trying a shorter release
> cycle -- to change from 9 months to 6 months [0]. There are, however,
> repercussions on how we manage stable and possible LTS releases.
> 
> I start this thread hoping it's clearer that downstream consumers like
> distributions and individual packagers can voice their opinions. I've
> CC'ed some people I can think of who might be interested in this topic.
> Feel free to CC more people.
> 
> We don't have LTS scheme at the moment. Let me start with current
> scheme for stable releases.
> 
>  - Release from xen-unstable every 9 months.
>  - Maintain last 3 releases as stable releases.
> 
> So in effect, every stable release is maintained for at least 27
> months.
> 
> When we switch to 6 months release cycle, if we stick with the same
> scheme (last 3 releases as stable releases), every stable release is
> only maintained for 18 months. It's too short for downstream
> consumers.
> 
> Ian proposed a scheme [1] in reply to [0]. In short, that scheme
> proposes we pick every Nth release as LTS. He also proposed N=4 in the
> case of 6 months release cycle.
> 
> (FWIW I think N=4 is a sensible suggestion.)
> 
> I can think of some open questions.
> 
> 1. How long should each LTS release be maintained?
> 
> Here are my two cents, there are two fundamental criteria for deciding
> how long a LTS is supported: a) it can't be shorter than what we
> already have (27 months); b) at any given time there must be at least
> one LTS release available to downstream.
> 
> With these in mind and N=4, I would say supporting LTS for at least
> 2.5 years (5 release cycles) should be the minimal requirement. As for
> the upper limit, I don't know. Linux has LTS supports ranging from 2.5
> years to 5.5 years [2]. Another data point is Debian LTS is supported
> for 5 years [3].
> 
> Steven would like to see LTS be supported for 4 year full support + 1
> year security fix only [4]. I'm not sure how feasible this is with
> current set of maintainers (in fact, only Jan and Ian at the
> moment). But in the end there is nothing that prevents other people
> from stepping up and taking over the tree. We saw that with Xen 3.4
> already.

Could we just keep the same general scheme of "maintain 3 releases"?

If the most recent release was *not* an LTS, we'd have one release + 2
LTSes.  If the most recent release *was* an LTS, we'd have 3 LTSes --
the last one supported until a non-LTS release came out.  If LTSes
happen every 4 releases, then we'd get an LTS release every 2 years,
giving is 4.5 years support (54 months).

 -George