Kustomize Configuration Management

Kustomize is a free and open-source configuration management tool designed specifically for managing Kubernetes resource configurations (YAML manifests). Originally developed by Google as an independent project (created by Jeff Regan and others) and first released in 2018, Kustomize was later integrated into kubectl (since Kubernetes 1.14, 2019) as a built-in feature, making it the default configuration management tool for Kubernetes. Key features: template-free: unlike Helm or other templating engines, Kustomize does not use templates. Instead, it works with plain, valid Kubernetes YAML manifests and overlays. This means base configurations remain standard YAML that can be applied directly with kubectl apply. kustomization.yaml: the core concept is a kustomization.yaml file that declares which resources to include and how to customize them. A kustomization file lists resources (deployments, services, configmaps), and applies patches, labels, namespaces, name prefixes/suffixes, and other transformations. Overlays: Kustomize uses a base-and-overlay pattern. A base directory contains shared resource definitions, while overlay directories contain environment-specific customizations (e.g., dev, staging, production). Overlays can add resources, change replicas, set environment-specific images, and modify any field via strategic merge patches or JSON patches. Generators: ConfigMap and Secret generators create these resources from files or literals, with optional hashing to trigger rollouts when content changes. Name reference rewriting: when a generated ConfigMap name changes (due to content hashing), Kustomize automatically updates references in Deployments and StatefulSets. Components: reusable pieces of configuration that can be included in multiple bases or overlays. Built into kubectl: run kubectl apply -k or kustomize build. Go. Apache-2.0.