RevisionName templating and substitution.

[muscionig]

DRAFT up for discussion

Changes

This PR adds support for replacing the revisionName in the PrometheusMetric field. I discussed this with @skonto in the slack channel and it seemed a necessary feature to separate the scaling of different revisions. This is still in draft, it is missing unit tests and complete functional testing.

Minor Changes

• 🎁 adds a templating feature that allows to substitute the revisionName under the PrometheusQuery annotation. The feature uses template and sprig. I thought of using sprig to make sure the variable substitution is solid and to potentially support additional substitutions in the future.

Usage:

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: metrics-test
spec:
  template:
    metadata:
      labels:
        app: metrics-test
      annotations:
        ...
        autoscaling.knative.dev/metric: "http_requests_total"
        autoscaling.knative.dev/prometheus-query: "sum(rate(http_requests_total{pod=~\"{{ .revisionName }}.*\"}[1m]))"

I tested this with Istio

Output of the controller:

### service with no substitution
autoscaler-keda 2024/11/20 06:42:59 PrometheusQuery rendered: sum(rate(http_requests_total{}[1m]))                                    
autoscaler-keda {"severity":"INFO","timestamp":"2024-11-20T06:42:59.698756553Z","logger":"hpaautoscaler","caller":"controller/controller.go:548","message":"Reconcile succeeded","commit":"6f54184-dirty","knative.dev/controller":"knative.dev.autoscaler-keda.pkg.reconciler.autoscaling.hpa.Reconciler","knative.dev/kind":"autoscaling.internal.knative.dev.PodAutoscaler","knative.dev/traceid":"12a29044-6fe7-442b-a31c-7913633203cf","knative.dev/key":"metrics-test-istio/metrics-test-istio-00001","duration":"10.55125ms"}


### service with substitution
autoscaler-keda 2024/11/20 06:43:12 PrometheusQuery rendered: sum(rate(http_requests_total{pod=~"metrics-test-00001.*"}[1m]))
autoscaler-keda {"severity":"INFO","timestamp":"2024-11-20T06:43:12.122399087Z","logger":"hpaautoscaler","caller":"hpa/keda_hpa.go:98","message":"Creating Scaled Object \"metrics-test-00001\"","commit":"6f54184-dirty","knative.dev/controller":"knative.dev.autoscaler-keda.pkg.reconciler.autoscaling.hpa.Reconciler","knative.dev/kind":"autoscaling.internal.knative.dev.PodAutoscaler","knative.dev/traceid":"0fbaf41d-ecbf-4cf5-b417-64b2543e2e7f","knative.dev/key":"default/metrics-test-00001"}

Scaling of only one service:

/kind documentation
/kind enhancement

[knative-prow]

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[knative-prow]

Hi @muscionig. Thanks for your PR.

I'm waiting for a knative-extensions member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[skonto]

Sprig has more functions but for now let's keep this minimal, let's just use the Golang templates.

[skonto]

After updating go.mod it is required to run ./hack/update-deps.sh.

[skonto]

As a side note Serving supports byo revision names instead of being auto-generated.

kind: Service
metadata:
  name: hello
spec:
  template:
    metadata:
      name: hello-1

If you want to change that service above, then you need to manually change hello-1 to something else. PA name is always the same as with revision name.

[skonto]

@muscionig let's proceed with this and add some tests to verify that it works as expected. Next we can add some docs.