Versioning of images

[Bastian Blank <waldi@debian.org>]

Moin

We all know that versioning stuff is pretty hard problem.  I thought the
current state would be okay, but with time I found some flaws in it.

What do we want from a version?

- A user should be able to tell what's in it, which we do by using a
  date.
- It should contain some monotonic increasing value to distinguish
  between different builds on the same date.
- Development builds should have something distinct in it.

We currently have:

- Amazon EC2 uses 2015-06-07-12-27, aka date plus time.
- Google Cloud uses 20181219 and 20181219a.
- MS Azure uses 20181219.0 or 201812190 for the internal version.

This version is part of our name, but also needs to follow some more or
less strict rules by our providers in how it selects the latest image
for an user:

- Amazon EC2 seems to not have any grouping of community images, nor
  does it sort them in a particular way.  Apart from that it looks just
  like a string.
- Google Cloud just uses the last image added to an image family, the
  image name itself is just a string and does not matter.
- MS Azure uses a real versioning schema with a version consisting of
  three 32-bit numbers.  The user usualy selects an image sku and gets
  the image with the highest version available.

To accomodate this, I'll propose for the textual version:

- The first part of the version depends on the build type.
  - For release images, it will be the current date as number (e.g.
    20181219).
  - For development images built on the CI, it will be the namespace (if
    the repo is /waldi/debian-cloud-images, it will be "waldi").
  - For development images built with make, it will be "manual".
- The second part will be just the CI pipeline IID (the ID relative to
  the current project, so it won't get too large).  This ID is automatic
  and monotonic increasing for a particular project.

This gives as versions:

- 20181219.324
- waldi.324
- manual.0

This also maps easily into Azure versions:

- 0.20181219.324
- 0.0.324

Regards,
Bastian

-- 
Another dream that failed.  There's nothing sadder.
		-- Kirk, "This side of Paradise", stardate 3417.3