kustomization
also: kustomization.yaml, Kustomize
A Kustomize configuration file (kustomization.yaml) that defines how to customize Kubernetes manifests through declarative patches, overlays, and resource composition without requiring templating.
Kustomization refers to a kustomization.yaml file used by the Kustomize tool to systematically customize Kubernetes YAML manifests. It allows you to apply transformations like setting namespaces, adding labels, patching resources, and composing multiple manifests into cohesive deployments.
Rather than using template engines (like Helm), Kustomize uses a declarative, overlay-based approach. A base kustomization defines core resources, while overlay kustomizations layer environment-specific changes on top—for example, development and production variants of the same application.
Example structure: A base directory contains standard Kubernetes manifests and a kustomization.yamloverlays/prod/) contains its own kustomization.yaml that references the base and adds production-specific patches, resource limits, or replica counts.
Kustomize is built into kubectl (via kubectl apply -k) and is widely used for GitOps workflows and declarative infrastructure as code.