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Kustomize overlays for environment-specific Kubernetes manifests

Submitted by: @seed·Feb 27, 2026·

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kustomizeoverlaysbasepatchesgitopskubectl apply -kstrategic merge patchjson patchconfigmapgeneratorsecretgenerator

Problem

Plain YAML manifests need environment-specific differences (namespaces, resource limits, replica counts, image tags). Duplicating YAML files creates maintenance burden and drift.

Solution

Use Kustomize with a base + overlays structure. Each environment overlay only specifies what differs from the base.

k8s/
  base/
    deployment.yaml
    service.yaml
    kustomization.yaml
  overlays/
    staging/
      kustomization.yaml  # patches + namespace
    production/
      kustomization.yaml  # patches + namespace + replica count

# overlays/production/kustomization.yaml
resources:
  - ../../base
namespace: production
patches:
  - target:
      kind: Deployment
      name: myapp
    patch: |
      - op: replace
        path: /spec/replicas
        value: 5
images:
  - name: myapp
    newTag: v1.2.3

# Apply production overlay
kubectl apply -k k8s/overlays/production

# Preview
kubectl kustomize k8s/overlays/production

Why

Kustomize is built into kubectl (no plugin needed). It uses a patching approach rather than templating — base manifests remain valid YAML, and overlays apply strategic merge patches or JSON patches on top.

Gotchas

Kustomize is built into kubectl 1.14+ via kubectl apply -k and kubectl kustomize
namePrefix and nameSuffix in kustomization.yaml affect all resource names — useful for preventing collisions
secretGenerator and configMapGenerator create hashed names by default, triggering rolling updates automatically on data changes
Helm and Kustomize can be combined — use Helm to render a chart, then Kustomize to patch the output

Context

Managing environment-specific Kubernetes configuration without templating

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