Kubernetes CRDs & Operators: Extending the API

A 10-episode series covering Kubernetes Custom Resource Definitions and Operators — from what a CRD is through building a production operator and shipping CRD-based systems at scale.

Who it’s for: Platform engineers, SREs, and Kubernetes practitioners (2–5 years experience) who know how to use Kubernetes but want to understand how to extend it. No prior operator or controller experience required.

By the end: understand the full CRD lifecycle — define schema, write a controller with controller-runtime, handle versioning with conversion webhooks, validate with CEL, and ship production-ready operators with proper finalizers and status conditions.

Series complete — all 10 episodes published.

Part 2 of the Kubernetes learning arc on linuxcent.com. Part 1: Kubernetes History →

Episodes

EP	Title	Tier	Status
EP01	What Is a Kubernetes CRD? How Custom Resources Extend the API	Beginner	Published
EP02	CRDs You Already Use: cert-manager, KEDA, and External Secrets Explained	Beginner	Published
EP03	Kubernetes CRD Schema Explained: Versions, Validation, and Status Subresource	Beginner–Intermediate	Published
EP04	Write Your First Kubernetes CRD: A Hands-On YAML Walkthrough	Intermediate	Published
EP05	Kubernetes CRD CEL Validation: Replace Admission Webhooks for Schema Rules	Intermediate	Published
EP06	The Kubernetes Controller Reconcile Loop: How CRDs Come Alive at Runtime	Intermediate	Published
EP07	Build a Simple Kubernetes Operator with controller-runtime and kubebuilder	Advanced	Published
EP08	Kubernetes CRD Versioning: From v1alpha1 to v1 Without Breaking Clients	Advanced	Published
EP09	Admission Webhooks: Validating and Mutating Requests Before They Reach etcd	Advanced	Published
EP10	Kubernetes CRDs in Production: Finalizers, Status Conditions, and RBAC Patterns	Advanced	Published

Learning Arc

BEGINNER ────────────────────────────────────────────── ADVANCED
EP01  EP02  EP03  EP04  EP05  EP06  EP07  EP08  EP09  EP10
│     │     │     │     │     │     │     │     │     │
What  Using CRD   Write CEL   Ctrl  Build CRD   Adm.  Prod
is a  real  anat- first valid loop  oper- vers- web-  patterns
CRD?  CRDs  omy   CRD   ation       ator  ioning hooks

Start with EP01: What Is a Kubernetes CRD? →