2.9 KiB
RFC-0005 Extend supported list of image automation marker reference attributes
Status: provisional
Creation date: 2021-12-16
Last update: 2022-01-25
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 more complex to build. (new kubernetes object, new controller)
This raise the question on should this feature to be included in flux or not.
Design Details
Two options are possible here:
- Only modify the Image Automation Controller to make it read ImagePolicies spec and compute attributes
- Modify the Image Reflector Controller, to extract the attributes, stores them in the status and update the Image Automation Controller to use this new data storage.
The second option seems to be preferable to separate concerns.
A simple option would be to allow multiple capture group in the filter in the ImagePolicy:
extract: $ts
pattern: ^pr-(?P<pr>.*)-(?P<ts>\d*)-(?P<sha1>.*)$
And then to modify the Image Automation Controller 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 capture an attribute with a name like tag or name (already defined
by flux core), then the original value will be kept and a warning should show on the
Image Reflector Controller logs.
As reminder, here is the definition for those default attributes:
- tag: the full tag string
- name: the image name
Implementation History
not implemented yet