Allow duration format used in Kubernetes API machinery

[MattiasAng]

Fixes #300 to allow duration format commonly used across Kubernetes operators.

While this could potentially be fixed in upstream github.com/santhosh-tekuri/jsonschema I think this validation is very much up to the interpretation of the RFC and it would probably require an upgrade to v6 which has changed APIs in the package and would require a lot of refactoring.

[yannh]

Hi @MattiasAng , are you saying that upgrading to v6 of the schema validation library would fix this? Eventually we probably would need to do that work anyway... Thanks!

EDIT: I see :( still I'd rather update the library rather than add workarounds to be honest :/

[MattiasAng]

@yannh No, it wouldn't solve the issue as they both interpret the RFC differently. So rephrasing a bit;

If we try and get this added to the jsonschema package and it gets merged it would probably be on the v6 version which would require a bigger refactoring of kubeconform validation steps. Considering the jsonschema package is not specific to Kubernetes I've got a feeling that it wouldn't be merged, but even if it was it would require considerably more work than just updating the version of the current module used.

If you think this workaround is not acceptable I'm currently swamped with other things that I wouldn't have time to take on trying to get this in to the jsonschema package, so I'll let someone else pick that up in that case and we'll use my fork for now.

[yannh]

@MattiasAng can you help me understand, essentially Kubernetes accepts some duration formats that are not part of the spec / or not part of the implementation of the spec in gojsonschemas? Could you expand a bit on those differences? 🙏

[yannh]

@MattiasAng I started a v6 branch, but am hoping for a cosmetic improvement first santhosh-tekuri/jsonschema#211 before I merge. I am also not completely sure I got it right just yet 😅 https://github.com/yannh/kubeconform/compare/jsonschemav6?expand=1

If this is a case of Kubernetes not implementing the spec correctly, and accepting input that is not, fundamentally, valid json schema, I think your patch would make sense, also it seems well-tested and simple enough...

[MattiasAng]

@yannh Sorry, I gave a bit more context in the issue and code comment so I can understand that the pull request itself is a bit confusing.

Yes, essentially Kubernetes API machinery package is not implementing duration according to ISO8601 where JSON schema uses RFC3339 Appendix A which is based on ISO8601. JSON Schema expects all time durations to start with P while API Machinery for Kubernetes (which most custom operators use) expects a format such as 5m or 5 min which is either parsed by time.ParseDuration (which I used) or Scala duration format which doesn't match against RFC3339.

A bit annoying considering they use the formatting for datetime and date from RFC3339.

So in short, unless the maintainers of JSONschema package want to be non-compliant with RFC3339 I don't see how this could be upstreamed. 😄