28th Feb 2018 by Kurt Garloff & Daniela Ebert

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New Linux image naming and registration policies

Introduction

Currently, for each Linux image, there are two series of images, one with a datestamp (e,g, _20180106_0) and one with a _latest name which gets renamed to _prevN and hidden upon a new _latest image registration. We have followed a roughly monthly update schedule (aligning with the Windows world) for the datestamp images and the _latest images while pushing out additional _latest images in between occasionally based on major improvements, bug fixes or security issues.

The rationale was to both offer images that can be used long-term (for customers that may not yet have adopted continuous deployment models) as well as a possibility for customers to have current images (which don't need a lot of online updates to be secure).

The disadvantage of the current approach is that a lot of old images are stored on the platform and (more importantly) cause the image list to become larger and larger, confusing customers and causing a glance image-list to require more than 10s of time (and at some point even fail for clients that don't properly handle REST pagination).

We found a lot more customers using the _latest images and thus propose to completely drop the images with a date stamp. We have created a possibility to hide older images from the _prevN series in a way that they can be continued to be used IF referenced by image UUID.

Actions

To achieve the goal of cleaning up our public image catalog, we will hide or remove old images.

In detail:

• We only delete ancient images (from 2016) which are not in use any more or don't work well any longer.
• We hide the images that still carry minor versions which we stopped using. (e.g. Standard_CentOS_7.3_latest will be hidden, please use Standard_CentOS_7_latest instead)
• We will keep two versions of each image visible, the latest and the previous one.
• All other old images will be hidden, not deleted, meaning that the images can still be used if the user has taken a note of the image UUID (or requests that information from our support organisation). Note that neither renaming from _lastest to _prev nor the final rename to _DATE and the connected hiding will change the image UUID.

So the images each go through the cycle:

+-------+       +-------+       +-------+
|Image1 |       |Image1 |       |Image1 |
|visible|       |visible|       |hidden |       (no more
|_latest|  ->   | _prev |  ->   |_DATE1 |   ->   changes)
| UUID1 |       | UUID1 |       | UUID1 |
+-------+       +-------+       +-------+

                +-------+       +-------+       +-------+
                |Image2 |       |Image2 |       |Image2 |
                |visible|       |visible|       |hidden |       (no more
                |_latest|  ->   | _prev |  ->   |_DATE2 |   ->   changes)
                | UUID2 |       | UUID2 |       | UUID2 |
                +-------+       +-------+       +-------+

                                +-------+       +-------+       +-------+
                                |Image3 |       |Image3 |       |Image3 |
                                |visible|       |visible|       |hidden |
                                |_latest|  ->   | _prev |  ->   |_DATE3 |
                                | UUID3 |       | UUID3 |       | UUID3 |
                                +-------+       +-------+       +-------+

                                                 ...

The cycling happens at least once a month, so _latest will be at max 1 month old, _prev max 2 months, where as the _DATE images (only referencable by UUID) declare their birth date in their name.

Benefits

• The amount of (new) images that are registered and stored on the platform is cut by a factor of two.
• The images showing up in the image catalog is reduced by an order of magnitude, avoiding confusion and speeding up the catalog operations.
• The Linux images are handled more similarly to the Windows images.
• Communication is easy: Images by name _latest are always latest and Images by UUID are stable and aging (similar to content-based addresing as used by git).

Customer recommendations

After implementation of the new policies, users have the same choices as before: Using latest or fixed images. The choice can be done by

• Always using our latest images by referencing it by the name _latest.
• Using the the previous images by referencing it by the name _prev.
• Staying on the same image by referencing it by UUID.

We expect most cloud users to have mechanisms in place where they can handle change -- they are typically best served by always using our _latest images. However, we acknowledge that there are valid cases where users can not deal with OS maintenance updates well and thus we offer the ability to reference images (current ones as well as old ones) by UUID. While we hide the old images after some time, they remain available by UUID for a long time.

Timeline

We will introduce this new policy with the image next publish at 15th of March 2018. This will also affect the BareMetal images, which currently have only datestamps and will then only have a public _latest and _prev and hidden datestamp images.

We will then clean up and hide the older images in the second half of March.