# Bookstore — Part 06 ch.04 "Autoscaling": KEDA event-driven scaling of the
# payments-worker on RabbitMQ queue depth (the canonical scale-to-zero case).
#
# A KEDA ScaledObject does NOT replace the HPA — it MANAGES one. KEDA's
# operator creates a hidden HPA whose scaleTargetRef is the payments-worker
# Deployment (19-) and an external-metrics adapter feeding it the live
# "orders" queue length. The HPA then runs the SAME algorithm as 82-:
#   desiredReplicas = ceil[ currentReplicas * (queueLength / value) ]
# Below `minReplicaCount` (here 0) KEDA, not the HPA, scales the Deployment to
# zero when the trigger is inactive (queue ≤ activationValue for the cooldown),
# and back up from zero the moment a message arrives — the thing a plain HPA
# cannot do (an HPA never scales to/from 0).
#
# Flow: orders (14-) publishes -> RabbitMQ "orders" queue grows ->
#   KEDA scaler reads the queue length -> drives the managed HPA ->
#   payments-worker (19-) scales out -> consumers drain the queue ->
#   queue empties -> KEDA scales back toward 0. (queue name "orders" is a
#   const shared by app/orders/main.go and app/payments-worker/main.go.)
#
# !!! CRD-BACKED — intrinsic dry-run behaviour (exactly like 18-/51-/70-/80-)
# `ScaledObject` and `TriggerAuthentication` are KEDA CRDs (keda.sh/v1alpha1),
# NOT built-in kinds. Without KEDA installed, a client dry-run prints
#   no matches for kind "ScaledObject" in version "keda.sh/v1alpha1"
# (and the same for TriggerAuthentication) — EXPECTED, identical to 70-/80-.
# A whole-dir client dry-run prints this for THIS file only and continues;
# every built-in object (incl. 19-/82-) still validates. Schema below verified
# against the KEDA keda.sh/v1alpha1 ScaledObject API and the KEDA RabbitMQ
# scaler reference (metadata keys: protocol, queueName, mode, value,
# activationValue, hostFromEnv).
#
# Requires (to actually apply, not just read):
#   - KEDA installed (operator + CRDs + metrics adapter) via Helm — NOT a
#     `releases/latest/download/keda-<ver>.yaml` URL (that 404s the moment a
#     newer KEDA ships: `latest/` resolves to the newest tag but the filename
#     is version-pinned). Helm, like every other Part 06 add-on:
#       helm repo add kedacore https://kedacore.github.io/charts
#       helm repo update
#       helm install keda kedacore/keda \
#         --namespace keda --create-namespace --wait
#     (installs into the `keda` namespace — its own ns, NOT restricted; fine)
#   - 13-rabbitmq.yaml + 19-payments-worker-deploy.yaml applied
#   - the `rabbitmq-conn` Secret below (AMQP URL for the scaler to query the
#     broker). It is NOT db-credentials (16-) — that holds Postgres creds; the
#     worker has no DB. Created inline here so this file is self-contained.
# Apply (KEDA-equipped cluster only):
#   kubectl apply -f examples/bookstore/raw-manifests/83-keda-scaledobject.yaml
#   kubectl get scaledobject,hpa -n bookstore   # KEDA created an HPA for you
#   kubectl describe scaledobject payments-worker -n bookstore
---
# AMQP connection string for the KEDA scaler ONLY (it queries the broker for
# the queue length). guest/guest matches 13-rabbitmq.yaml + 19-'s AMQP_URL.
# Opaque Secret; stringData is base64-encoded by the API server on write.
apiVersion: v1
kind: Secret
metadata:
  name: rabbitmq-conn
  namespace: bookstore
  labels:
    app: payments-worker
    app.kubernetes.io/part-of: bookstore
type: Opaque
stringData:
  # AMQP protocol endpoint (the RabbitMQ scaler with protocol: amqp reads the
  # queue length over AMQP, no management plugin/HTTP needed).
  host: "amqp://guest:guest@rabbitmq.bookstore.svc.cluster.local:5672/"
---
# TriggerAuthentication wires the Secret above into the trigger so the
# connection string is never inlined in the ScaledObject (KEDA best practice).
apiVersion: keda.sh/v1alpha1
kind: TriggerAuthentication
metadata:
  name: rabbitmq-trigger-auth
  namespace: bookstore
  labels:
    app: payments-worker
    app.kubernetes.io/part-of: bookstore
spec:
  secretTargetRef:
    - parameter: host                # the RabbitMQ scaler's `host` parameter
      name: rabbitmq-conn            # <- the Secret above
      key: host
---
apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: payments-worker
  namespace: bookstore
  labels:
    app: payments-worker
    app.kubernetes.io/part-of: bookstore
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: payments-worker            # the real Deployment (19-)
  pollingInterval: 15                # how often KEDA checks the queue length (s)
  cooldownPeriod: 60                 # wait 60s of inactivity before scaling to 0
  minReplicaCount: 0                 # SCALE TO ZERO when the queue is idle
  maxReplicaCount: 10                # bounded by the namespace ResourceQuota (00-)
  # advanced.horizontalPodAutoscalerConfig.behavior would tune the MANAGED
  # HPA's scale velocity (same knobs as 82-'s behavior); omitted = KEDA's
  # sensible defaults, kept simple for the teaching example.
  triggers:
    - type: rabbitmq
      metadata:
        protocol: amqp               # query queue length over AMQP (5672)
        queueName: orders            # the queue orders publishes / worker consumes
        mode: QueueLength            # scale on number of messages (not rate)
        value: "20"                  # target msgs/replica: desired = ceil(len/20)
        activationValue: "1"         # scale 0 -> 1 as soon as ≥1 message waits
      authenticationRef:
        name: rabbitmq-trigger-auth  # the TriggerAuthentication above