flux2/rfcs/0005-managed-attributes-image-automation/README.md

RFC-0005 Extend supported list of image automation marker reference attributes

Status: provisional

Creation date: 2021-12-16

Last update: 2021-12-16

Summary

Flux should allow referencing more metadata in the image automation Setters strategy.

Motivation

Some automation or observability tools can use label to identify better a kubernetes object. It can be linked to a version, a date, a code origin... For multiple reason, the image tag can reflect poorly this data. An example can be given by the image reflector controller which can extract a part of the tag and use it to sort and select the correct one.

Goals

This RFC aims to describe

• A way to extract such additional attributes from the image tag.
• Use those new attributes to update the kubernetes object.

Non-Goals

This RFC will focus on Image Automation Controller and Image Reflector Controller.

It is a non goal to keep in sync the attributes if the kubernetes object is updated manually.

Proposal

User Stories

As a user, I can update the filter pattern on the image policy object to capture additional data. Then, I can reference the name of the captured group in the comment of a kubernetes object so that the attribute linked to this comment can be updated.

Alternatives

An alternative would be to build a mutation web hook which would be able to filter all object and interact with them directly.

It would be more generic, more customizable and safer (fix the manual update use case) to create such mutation web hook, but will be heavier to build. (new kubernetes object, new controller)

This raise the question on should this feature to be included in flux or not.

Design Details

Simple update on the image automation controller should be enough. Today a filter in the image policy is like:

    extract: $ts
    pattern: ^pr-(?P<pr>.*)-(?P<ts>\d*)-(?P<sha1>.*)$

It is possible to modify the image automation to take comment like:

  # {"$imagepolicy": "{namespace}:{imagepolicy}:{attributes}"

with attributes a name of a capture group on the pattern.

From previous pattern example, accepted attributes will be:

• pr
• ts
• sha1

If a user try to use an attribute name like tag or name which is already defined by flux core, then the original meaning will still be kept :

• tag: the full tag string
• name: the image name

Implementation History

not implemented yet