Summary of "DAY-40 | KUBERNETES CUSTOM RESOURCES | CUSTOM CONTROLLER | DEEP DIVE & DETAILED EXPLANATION | #k8s"

Summary of Video

DAY-40 | KUBERNETES CUSTOM RESOURCES | CUSTOM CONTROLLER | DEEP DIVE & DETAILED EXPLANATION

Key Technological Concepts Covered

1. Kubernetes Custom Resource Definitions (CRDs)

CRDs allow users to extend the Kubernetes API by defining new resource types beyond the native ones (e.g., Deployment, Service, Pod).
A CRD is a YAML manifest submitted to Kubernetes that defines the schema and validation rules for a new custom resource.
Example: Istio’s VirtualService is a custom resource validated against its CRD.

2. Custom Resources (CRs)

Instances of the CRD, created by users to leverage extended Kubernetes capabilities.
CRs are validated against their CRD to ensure correctness before creation.

3. Custom Controllers

Native Kubernetes resources like Deployments have built-in controllers managing their lifecycle. Similarly, custom resources require custom controllers.
A custom controller watches for changes in custom resources and performs necessary actions to implement the desired state.
Without a controller, a custom resource does nothing (similar to an Ingress resource without an Ingress controller).
Custom controllers are typically deployed by DevOps engineers alongside CRDs.

4. Actors in the Process

DevOps Engineer: Responsible for deploying CRDs and custom controllers to extend Kubernetes API and functionality.
Users (Developers or DevOps): Create custom resources based on CRDs to use the extended features.

5. Use Cases & Examples

Applications like Istio (service mesh), Argo CD (GitOps), Keycloak (IAM/OAuth), Prometheus (monitoring), and others extend Kubernetes via CRDs and custom controllers.
These tools add advanced capabilities (security, traffic management, identity, monitoring) not available in native Kubernetes resources.

6. How Kubernetes Supports Extensibility

Kubernetes provides a mechanism to extend its API rather than modifying core components for every new feature.
This extensibility is critical due to the vast ecosystem of tools and custom solutions built on Kubernetes.

7. Writing Custom Controllers

Most commonly written in Golang, as Kubernetes itself is written in Go and the client-go library provides a rich API to interact with Kubernetes.
Other languages like Python and Java are also supported but Go remains the preferred choice.
Controllers use watchers and event handlers to monitor resource changes and reconcile state.
Frameworks like controller-runtime and operator-sdk simplify building controllers/operators.

8. Practical Guide & Demo

The video references Istio’s GitHub repository as a real-world example of CRDs and custom controllers.
Installation typically involves deploying CRDs and controllers via Helm charts or Kubernetes manifests.
Commands like kubectl get crd show installed CRDs in the cluster.
DevOps engineers must also troubleshoot and debug issues related to custom resources and controllers by checking logs and resource status.

9. Comparison Between Native and Custom Resources

Both have resource definitions (schemas) that validate resource manifests.
Native resources have built-in controllers, whereas custom resources require separately deployed custom controllers.

Product Features / Tutorials / Guides Highlighted

Conceptual Deep Dive: Clear explanation of CRDs, CRs, and custom controllers and their interplay.
Practical Installation Guide: Using Helm charts to deploy Istio CRDs and controllers.
Development Insight: Overview of writing custom controllers using Go and client-go libraries.
Community & Ecosystem: Mention of CNCF projects (Istio, Argo CD, Prometheus, Crossplane, etc.) as examples of popular custom Kubernetes controllers.
Debugging Tips: Importance of understanding the installed custom resources and controllers, checking logs, and validating resource states.

Main Speakers / Sources

Abhishek: The sole presenter and instructor delivering the full explanation, tutorial, and practical demonstration.
References to:
- Istio GitHub repository and official documentation
- CNCF (Cloud Native Computing Foundation) projects and ecosystem
- Kubernetes official documentation and sample controller GitHub repository

This video serves as a comprehensive guide for DevOps engineers and Kubernetes users to understand how to extend Kubernetes functionality using custom resource definitions, custom resources, and custom controllers, with practical examples and pointers to further resources.