Kubernetes

Cluster API is an open-source Kubernetes subproject focused on declarative APIs and tooling for provisioning, upgrading, and operating multiple Kubernetes clusters. Developed by the Kubernetes SIG Cluster Lifecycle, it uses Kubernetes-style APIs and patterns to define cluster configuration and supporting infrastructure—including virtual machines, networks, load balancers, and VPCs—for consistent, repeatable deployments. Providers extend it to infrastructure platforms such as AWS, Azure, and vSphere, while kubeadm is provided as a built-in bootstrap and control-plane provider.

Crossplane is a Kubernetes-native, CNCF project for building cloud-native control planes without writing a custom control-plane implementation. Its extensible backend orchestrates applications and infrastructure across environments through declarative APIs, while its configurable frontend lets platform teams define schemas for internal infrastructure abstractions. It manages provider-backed managed resources (MRs), composite resources (XRs), and Compositions that package collections of infrastructure resources behind simpler interfaces. Kubernetes reconciliation continuously works toward the declared state through provider APIs, and custom functions can be developed as reusable building blocks within compositions.

Open Policy Agent (OPA) is an open-source, general-purpose policy engine and graduated Cloud Native Computing Foundation project. It uses the declarative Rego language to define rules and evaluates supplied policies and data in response to queries, returning decisions such as whether an API request is allowed, what cluster a workload may target, or which resource tags are required. Services can integrate with OPA through its Go SDK, Go API, REST API, or other documented integrations; OPA is also available as a CLI, container image, and binary. The videos specifically describe its use for Kubernetes admission policies and command-line validation before resources reach a cluster.

KCL is an open-source, constraint-based record and functional language for generating and managing configuration, including cloud-native and Kubernetes resources. It uses schemas, static types, constraints, rules, and isolated configuration blocks to model, validate, mutate, and organize configuration while reducing boilerplate; it can generate JSON and YAML or integrate with existing data. KCL supports configuration tooling such as formatting, linting, testing, documentation, package management, IDE extensions, and SDKs for several languages, and integrates with Kubernetes through tools including the Kubectl, Kustomize, Helm, and Crossplane KCL plugins. In Crossplane workflows, it can be used to develop composition functions as independent executable source code before embedding them into YAML at build time. The project is a CNCF Sandbox project and its implementation uses Rust and C, with support for native-code and WebAssembly compilation.

Kustomize is a Kubernetes configuration customization tool sponsored by the Kubernetes SIG CLI. It processes raw, template-free YAML without modifying the original files, using declarative kustomization files to combine resources, apply patches and labels, generate resources such as ConfigMaps, and create overlays for development, staging, and production variants. It can wrap separately managed Kubernetes and CRD files and reference external files without copying their full contents into a repository. The resulting YAML can be emitted with `kustomize build` and applied directly with `kubectl`; Kustomize is also integrated into kubectl.