Tool for Generating Trigger Schema

[SpiritZhou]

Proposal

Generating trigger metadata schema according to new declarative scaler configuration, which can be used for validation or other related improvement.

Input:
make generate-scaler-schemas [--keda-version][--specify-scaler][--outputfile]

Output:
scaler-metadata-schemas.yaml

Trigger metadata example:

kedaVersion: main
schemaVersion: 1
triggers:
    - type: prometheus
      metadata:
        - name: serverAddress
          type: string
        - name: query
          type: string
        - name: queryParameters
          type: string
          optional: true
        - name: threshold
          type: string
        - name: activationThreshold
          type: string
          optional: true
        - name: namespace
          type: string
          optional: true
        - name: customHeaders
          type: string
          optional: true
        - name: ignoreNullValues
          type: string
          optional: true
          default: "true"
        - name: unsafeSsl
          type: string
          optional: true
        - name: awsRegion
          type: string
          optional: true
          canReadFromAuth: true

Use-Case

No response

Is this a feature you are interested in implementing yourself?

Yes

Anything else?

No response

[wozniakjan]

the tricky part is that technically all metadata fields are string in the CRD definition despite the underlying type. The OpenAPI schema allows setting multiple types for a field, maybe we can leverage that in some way?
https://stackoverflow.com/questions/46472543/specifying-multiple-types-for-additionalproperties-through-swagger-openapi

We would likely need to change the map[string]string to map[string]any but this theoretically shouldn't be a breaking change.

[SpiritZhou]

Now the metadata parameters can be retrieved from the config, but there are two options in the following steps:

1. Attempt to merge the schemas to the ScaledObject schema. I've made several attempts in this direction, but there is no proper way to add them into the ScaledObjects CRD YAML. The major problem is that I can't find a way to validate the parameter combination of the trigger. I have tried using 'oneOf', but it is not working. If there is any other good approach, please let me know so that I can give it a try.
2. Save them as Trigger Metadata schema files and validate trigger metadata value on the webhook by loading these trigger metadata schemas at runtime.
   WDYT @JorTurFer @zroubalik @wozniakjan

[wozniakjan]

great findings @SpiritZhou! I think option 2 - a standalone schemas file should be sufficient. I personally would even descope the webhook and validation by kube-apiserver for now and only generate + publish the trigger schema file as part of the KEDA repository. That would already be a terrific improvement.