Kustomizeoverlays

Kustomize overlays are a method within Kustomize to customize Kubernetes manifests for different deployment environments without duplicating base configurations. They enable environment-specific changes by layering patches on top of a common base.

In Kustomize, a project consists of a base and one or more overlays. A base is a set of Kubernetes resources; an overlay applies patches or generators on top of that base to produce environment-specific manifests. Overlays are typically organized as separate directories (for example, overlays/dev, overlays/prod) that reference the shared base and contain their own patch files.

A typical overlay contains a kustomization.yaml that declares the resources it overlays (often referencing the base) and one or more patch files (via patchesStrategicMerge or patchesJson6902) to modify fields such as image tags, replica counts, or configuration data. Patches can adjust fields within existing resources or introduce environment-specific values without editing the base artifacts directly. Overlays may also include generators for ConfigMaps and Secrets, as well as common labels and other customization primitives.

Users render the final manifests with kustomize build or kubectl -k, which outputs the customized YAML ready for deployment. This workflow supports environment-specific configurations while preserving a single source of truth for base manifests.

Common elements in an overlay include patches to adjust images (for example, changing tags or registries), resource generators, and shared metadata such as commonLabels. Overlays promote reproducible deployments across development, testing, and production, though they require disciplined patch management to avoid drift or conflicts.