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Bases, Overlays and Patches

A directory with a kustomization.yaml is a kustomization. A base lists resources; an overlay lists a base as a resource and adds changes. BookNest's base is its application manifests, unchanged:

k8s/kustomization.yaml: the baseYAML
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources: [api-config.yaml, api-deployment.yaml, api-service.yaml, api-hpa.yaml, web.yaml,
  postgres.yaml, network-policies.yaml, gateway.yaml]

Transformers change every object (namespace, labels, namePrefix, images, replicas). Generators build ConfigMaps and Secrets and append a content hash to the name, rewriting references, so a changed value rolls the Pods. Patches edit chosen objects, as a strategic merge patch (partial YAML) or an RFC 6902 JSON patch (operations on paths). Overlays may not live inside their base, so BookNest's sit in overlays/staging and overlays/production.