# Bookstore — Part 04 ch.03 "Priority and preemption": the priority ladder.
#
# THREE cluster-scoped PriorityClass objects that rank Bookstore workloads for
# scheduling and preemption. PriorityClass is NOT namespaced (it is a
# cluster-wide object) — it has no `metadata.namespace`. A workload opts in via
# `spec.template.spec.priorityClassName: <name>`.
#
# Ladder (higher value = scheduled sooner, evicted/preempted later):
#   bookstore-data       1000000   postgres (the data tier — lose it, lose data)
#   bookstore-critical     100000   catalog / orders / storefront (user-facing)
#   bookstore-batch          1000   db-migrate Job / cleanup CronJob (deferrable)
#
# Why these exact gaps: the values only need to ORDER the tiers; the wide gaps
# leave room to slot future classes between them without renumbering. They are
# all FAR below the built-in `system-cluster-critical` (2000000000) and
# `system-node-critical` (2000001000) so Bookstore can never out-prioritise
# control-plane / node add-ons (CoreDNS, CNI, kube-proxy) — that is deliberate.
#
# globalDefault: NONE is true. A `globalDefault: true` class would silently
# apply to EVERY Pod cluster-wide that omits priorityClassName (including other
# namespaces) — too blunt and not ours to decide cluster-wide. Pods that do not
# name a class get priority 0 (or the cluster's existing global default), which
# is correct: lower than every Bookstore tier here, exactly as intended.
#
# Wiring (done in the workload manifests, see ch.03 hands-on):
#   20-postgres-statefulset.yaml   -> priorityClassName: bookstore-data
#   10-catalog-deploy.yaml         -> priorityClassName: bookstore-critical
#   11-storefront-deploy.yaml      -> priorityClassName: bookstore-critical
#   14-orders-deploy.yaml          -> priorityClassName: bookstore-critical
#   21-db-migrate-job.yaml         -> priorityClassName: bookstore-batch
#   22-cleanup-cronjob.yaml        -> priorityClassName: bookstore-batch
#
# Requires: nothing (cluster-scoped; apply before/independently of workloads).
# Apply:
#   kubectl apply -f examples/bookstore/raw-manifests/35-priorityclasses.yaml
#   kubectl get priorityclass | grep bookstore
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: bookstore-data
  labels:
    app.kubernetes.io/part-of: bookstore
value: 1000000                    # highest Bookstore tier: the stateful data
globalDefault: false
description: "Bookstore stateful data tier (postgres). Scheduled first, preempted last."
# preemptionPolicy defaults to PreemptLowerPriority: if no node fits, the
# scheduler MAY evict lower-priority Pods (batch, then critical) to make room.
---
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: bookstore-critical
  labels:
    app.kubernetes.io/part-of: bookstore
value: 100000                     # user-facing services (catalog/orders/storefront)
globalDefault: false
description: "Bookstore user-facing services. Above batch, below the data tier."
---
apiVersion: scheduling.k8s.io/v1
kind: PriorityClass
metadata:
  name: bookstore-batch
  labels:
    app.kubernetes.io/part-of: bookstore
value: 1000                       # deferrable batch (migration Job / cleanup CronJob)
globalDefault: false
# Never preempt anything to run batch work — batch can simply wait for capacity.
# (It can still BE preempted by the higher tiers above; that is intended.)
preemptionPolicy: Never
description: "Bookstore deferrable batch. Never preempts others; yields under pressure."