How to manage Kubernetes manifests across environments with Kustomize

Managing manifests with Kustomize

Kustomize customizes raw Kubernetes manifests through a base plus overlays model, with no templating language. A base holds common resources; each overlay patches the base for a specific environment. Kustomize is built into kubectl, so no extra tooling is required.

Prerequisites

• Existing Kubernetes YAML manifests.
• kubectl (which bundles kustomize) installed.

Steps

1. Create a base

Place shared manifests in base/, for example deployment.yaml and service.yaml.

2. Add a kustomization file

# base/kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - deployment.yaml
  - service.yaml

3. Create environment overlays

# overlays/prod/kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
namePrefix: prod-
namespace: prod
resources:
  - ../../base

4. Patch resources per environment

Increase replicas only in prod with a strategic merge patch:

patches:
  - target:
      kind: Deployment
      name: myapp
    patch: |
      - op: replace
        path: /spec/replicas
        value: 5

5. Generate ConfigMaps

Generate config with a content hash so pods roll on change:

configMapGenerator:
  - name: app-config
    literals:
      - LOG_LEVEL=info

6. Build and apply

kubectl kustomize overlays/prod
kubectl apply -k overlays/prod

kubectl kustomize prints the rendered output for review before applying.

Verification

Run kubectl kustomize overlays/prod and confirm the name prefix, namespace, and replica count reflect the overlay. Apply and verify with kubectl get deploy -n prod that the rendered objects exist as expected. A dev overlay should produce different values from the same base.

Next Steps

Use the same base across many overlays, add images transformers to set tags per environment, and feed Kustomize output into Argo CD so GitOps drives every environment from one base.