Components & reuse

Optional, composable feature sets.

A component is a reusable, optional slice of configuration you can mix into multiple overlays — the answer to “these three environments all need the monitoring sidecar, but not the others.” Unlike a base (which an overlay fully inherits), a component is composable: it contributes resources and patches that get applied wherever you list it, so you assemble an environment from a base plus the components it opts into.

apiVersion: kustomize.config.k8s.io/v1alpha1
kind: Component            # note: Component, not Kustomization
resources:
  - servicemonitor.yaml
patches:
  - path: add-metrics-port.yaml     # patch the base Deployment to expose metrics
---
# an overlay opts in:
#   components:
#     - ../../components/monitoring

Composition over duplication

Components let you express features independently and combine them per environment: a prod overlay might include the monitoring, network-policy, and hardening components while dev includes only monitoring. Because each component is a self-contained unit of resources-plus-patches, you avoid copy-pasting the same additions into every overlay. It is the Kustomize equivalent of feature toggles, done through composition rather than conditionals.