feat(wrt): auto-inject KEDA Temporal trigger metadata for per-version ScaledObjects

[nikoul]

Summary

Extends WorkerResourceTemplate auto-injection to populate the workerDeploymentName and workerDeploymentBuildId fields in KEDA ScaledObject triggers[*].metadata when the trigger type is "temporal". This unblocks using KEDA's Temporal scaler (kedacore/keda#7672) as the templated resource for per-version backlog scaling, as requested in #286.

Closes (or contributes towards) #286.

Motivation

For users who already run KEDA cluster-wide for non-Temporal workloads, KEDA owns the external.metrics.k8s.io APIService — only one external metrics provider can be installed per cluster. That makes the documented WRT-HPA + prometheus-adapter path unavailable: prometheus-adapter cannot co-exist with KEDA on the same APIService.

KEDA's recent Worker Deployment Versioning support (kedacore/keda#7672) makes it possible for a KEDA ScaledObject to scale a single worker version by querying Temporal Cloud directly with workerDeploymentName + workerDeploymentBuildId. WRT already supports templating arbitrary kinds (verified: spec.template is unstructured, SSA-applied, with a kind allow-list in the chart) and scaleTargetRef: {} auto-fill works recursively. The only missing piece was injecting the per-version identifiers into the KEDA trigger metadata — same source values the controller already injects into HPA External metric selectors, different JSON path.

Behaviour

For each templated resource that contains:

spec:
  triggers:
    - type: temporal
      metadata:
        workerDeploymentName: ""        # placeholder, any string value
        workerDeploymentBuildId: ""     # placeholder, any string value
        # ...other user-provided KEDA Temporal scaler metadata

the controller sets:

• workerDeploymentName ← wrt.Spec.EffectiveWorkerDeploymentName()
• workerDeploymentBuildId ← the per-version build ID

Injection is opt-in: the keys are only touched if already present in the template's metadata map (mirroring the existing metrics[*].external.metric.selector.matchLabels merge pattern). Non-temporal triggers in the same ScaledObject are left untouched.

Example

apiVersion: temporal.io/v1alpha1
kind: WorkerResourceTemplate
metadata:
  name: my-worker-scaler
  namespace: default
spec:
  workerDeploymentRef:
    name: my-worker
  template:
    apiVersion: keda.sh/v1alpha1
    kind: ScaledObject
    spec:
      scaleTargetRef: {}                     # auto-injected (versioned Deployment)
      minReplicaCount: 1
      maxReplicaCount: 10
      pollingInterval: 30
      triggers:
        - type: temporal
          metadata:
            endpoint: us-east-1.aws.api.temporal.io:7233
            namespace: my-temporal-ns
            taskQueue: my-task-queue
            workerDeploymentName: ""         # auto-injected
            workerDeploymentBuildId: ""      # auto-injected
            targetQueueSize: "10"
          authenticationRef:
            kind: ClusterTriggerAuthentication
            name: temporal-cloud-auth

The controller will stamp one ScaledObject per active worker version, each with the correct workerDeploymentBuildId, and delete them on sunset via the existing DeleteWorkerResources planner (kind-agnostic).

Implementation

• appendTemporalTriggerMetadata(spec, twdName, buildID) — new helper that walks spec.triggers[*], filters on type == "temporal", and sets the two keys if already present.
• autoInjectFields signature now takes twdName, buildID so it can pass them through. Behaviour for HPA / matchLabels / scaleTargetRef is unchanged.

Helm-side: adding ScaledObject to workerResourceTemplate.allowedResources + the controller's ClusterRole is left as a follow-up (or a separate commit in this PR if maintainers prefer). For users who want this today, they can add the entry to their chart values without further controller changes.

Tests

New TestAutoInjectFields_TemporalTriggerMetadata covers:

• injects when both keys present (empty string placeholders)
• overwrites stale values
• no-op when keys absent (opt-in semantics)
• non-temporal triggers are untouched (heterogeneous trigger array)
• scaleTargetRef: {} auto-fill still works on ScaledObject
• no panic when spec.triggers is absent

All existing tests still pass (go test ./...).

[CLAassistant]

All committers have signed the CLA.

[nikoul]

Hello @carlydf @jlegrone , I have tested and deployed this on our internal platform, and it seems to work well with KEDA 2.20.
Could you help move this PR forward? Thanks!

[Shivs11]

approved with some comments -- hoping you have a peek at them!

[jaypipes]

agree with @Shivs11 's review comments, plus left a couple of my own nits. @nikoul if you can address these shortly, we can approve and merge this PR today. thank you!

[jaypipes]

Thanks very much @nikoul :)