I am wondering if we could use the ISO 8601 Time intervals for this?

I'm also in support of using ISO 8601 time-intervals for this. I'm not sure if this is the intended way to use the spec, but I was thinking of something like follows (I assume @weyert might also be thinking along the same lines, if not please correct me here).

If we want a weekly time window that starts on a wednesday we could potentially do something like:

    - duration: 1w
      calendar:
        startTime: 2024-06-19 00:00:00
        timeZone: America/New_York

@alexewerlof do you see a use case which will not be fulfilled with the above approach (assuming this is intended way)

@anoopknayak yeah I'm aware of that format.

The general format for specifying repeating periods in ISO 8601 is:

R[n]/start/duration where

• The R character is for repetition (there's a R[n] convention for specifiying the number of repetitions indicated by n)
• The P character is for periods

Advantage

Compliance: no need to reinvent the wheel. Sticking to the standard means that we can potentially benefit from the wider ecosystem that can parse, lint, and generate this format. Moreover, it keep the OpenSLO standard shorter because we can just refer to ISO 8601.

Disadvantage

Harder to read: It requires some mental gymnastics and lookup the date and see which day of the week it is (2024-06-19 is a Wednesday), and then reason about the implicit behavior that if the date starts in the middle of the week, that day of the week is considered as the start of the period going forward. One could refer to the documentation for that to know that behavior, but I believe the whole point of YAML is to make it human-readable and I'm not sure if this format with those 2 extra steps is immediately approachable and intuitive. It works, but probably we could do better.

So if we want to specify weekly periods starting from 2024-06-19 00:00:00, we could write R/2024-06-19T00:00:00/P1W.

Subjectively, harder to read, but due to the advantages above, it might be better than my initial suggestion?

Note:
The ISO 8601 durations uses uppercase W which is different from the OpenSLO duration shorthand.

In the group discussion today we agreed that we don't change the spec but rather be more specific with an example about how it's done.

For this use case, we can mention:

If you're using a calendar-bound compliance period (SLO window) which uses weeks as the unit (e.g. 4w), the day of the start date will be used as the starting day of the period by convention.

e.g: if the start date is 2024-10-09 which is a Wednesday, this means a calendar-bound config of 4w will always look back from the start of Wednesday <=4 weeks ago.