kubebuilder

Kubebuilder is an open-source framework for building Kubernetes APIs and operators. It provides a set of tooling and project scaffolding that enables developers to create and manage custom resource definitions (CRDs) and their associated controllers in a consistent, testable way. The framework emphasizes native Kubernetes patterns and integrates with the Kubernetes API machinery.

Its core components include the Kubebuilder CLI for scaffolding projects, the controller-runtime library that implements common controller abstractions, and controller-gen for generating CRD manifests and OpenAPI schema from Go types. Kubebuilder projects typically organize API types, controllers, webhooks, and configuration manifests in a standard layout.

Typical workflow starts with kubebuilder init to bootstrap a project, followed by kubebuilder create api to add a new API group, version, and kind. Developers implement a Reconcile function in a controller, and use make test or make run against an envtest-enabled environment. The outcome is a Kubernetes operator that watches resources and reconciles desired state.

Markers such as +kubebuilder: markers on Go types influence CRD generation, including validation, subresources, and additional printer columns. RBAC rules can be generated via markers as well. The scaffolding also includes optional webhook support for validating and mutating resources.

History: Kubebuilder originated within the Kubernetes community and is maintained as part of the Kubebuilder project, closely associated with controller-runtime and the SIG API Machinery. It is one of several tools used to build operators and custom controllers for Kubernetes.