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How is Kustomize integrated natively into kubectl (kubectl apply -k)?

Infrastructure as Code (Terraform, Ansible) · Advanced level

Answer

Kustomize is integrated into kubectl. kubectl kustomize builds the rendered manifests, and kubectl apply -k applies a kustomization directory directly. This makes Kustomize usable without a separate templating command in simple workflows.

Technical explanation

kubectl kustomize is for rendering; kubectl apply -k is for applying.

GitOps controllers also render Kustomize internally.

Rendering in CI helps catch patch errors before sync or apply.

Keep source manifests or IaC definitions readable enough that reviewers can understand the final desired state.

Use overlays, modules, or roles for reuse, but keep environment-specific differences explicit and reviewable.

Validate generated output in CI before applying it through kubectl, Argo CD, Terraform, or Ansible.

Hands-on example

1. Create a Kustomize base and overlay for: How is Kustomize integrated natively into kubectl (kubectl apply -k)?

2. Base files:

base/deployment.yaml

base/service.yaml

base/kustomization.yaml

base/kustomization.yaml:

resources:

- deployment.yaml

- service.yaml

commonLabels:

app.kubernetes.io/name: payments

3. prod overlay:

resources:

- ../../base

namePrefix: prod-

namespace: payments-prod

images:

- name: ghcr.io/company/payments

newTag: 1.8.4

configMapGenerator:

- name: app-config

literals:

- LOG_LEVEL=info

patches:

- path: replica-patch.yaml

4. Render and apply:

kubectl kustomize overlays/prod

kubectl diff -k overlays/prod

kubectl apply -k overlays/prod

5. In GitOps, point Argo CD at overlays/prod and let it render, compare, and sync the desired state.

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