Advanced Filtering on Triggers

[nachocano]

Problem
We need more advanced filtering mechanisms than just exact match on Cloud Event types and sources.

Persona:
Event Consumer

Exit Criteria
Being able to configure advanced filters on triggers, either with CEL or some other language. E2E tests are necessary.

Time Estimate (optional):
~2 weeks, depending on how long the design discussions take.

[matzew]

@evankanderson while I like the idea, not sure if - for 0.6 we should introduce some "language" for advanced filters

[bbrowning]

I feel like something a bit more advanced is warranted. Even if it's not a full-blown expression language, it would be great to expand exact matching to fields in the Cloud Event data or allow some kind of basic wildcard matching.

To give some concrete samples of more advanced filtering I'd like:

• I want to receive all events from the K8s Event Source for namespace foo with Reason: RevisionReady
• I want to receive all events from the K8s Event Source for all Pods in namespace foo

[evankanderson]

Discussing with @lindydonna, it may make sense to actually go all the way in and then figure out what the commonalities are. (i.e. start with a full CEL expression or some equivalent, and then figure out that most customers end up writing "source like X, type is Y, and extracted field Z is present.")

The rationale being that once we have the advanced model, it's easy to implement the common items as syntactic sugar that gets expanded server-side, whereas if we started with smaller models, we may end up rewriting the filtering side multiple times. (And this way, the feature is "X is even easier" rather than "complicated use case Y is now more-possible without writing code".)

[grantr]

👍 Also consider that CEL may be a similar amount of work to prototype as homegrown simpler filtering. See https://github.com/grantr/cel-playground.

[nachocano]

Grant is taking care of this one!

/assign @grantr

[grantr]

/milestone v0.7.0

[lionelvillard]

Have you guys thought about providing the same capability to Subscription? @nachocano @grantr @evankanderson