Kubernetes Ingress Controller

# CHAPTER 11

Kubernetes Ingress Controller #

1. Introduction #

2. Learning Objectives #

• Identify the architectural flaws of relying solely on LoadBalancer services.

• Define what an Ingress and an Ingress Controller are.

• Understand path-based and host-based routing rules.

• Enable the NGINX Ingress Controller in Minikube.

• Author an Ingress YAML manifest.

3. Beginner-Friendly Explanation #

• The Old Way (LoadBalancers): You build 50 different physical front doors on the street. Each door goes straight to one business. It takes up the entire city block, and it's incredibly expensive to build.

• The Ingress Way: You build exactly ONE grand front entrance (The Ingress Controller). Inside the entrance sits a highly intelligent receptionist (The Ingress Rules).

• A customer walks in and says, "I am looking for website.com/blog." The receptionist checks their rulebook and sends them to Room 101.

• The next customer says, "I am looking for api.website.com." The receptionist sends them to Room 505.

4. Ingress vs. Ingress Controller #

• Ingress Controller: The actual software doing the heavy lifting (usually NGINX, HAProxy, or Traefik). It is a Pod running in your cluster that listens to external traffic. *Kubernetes does NOT come with an Ingress Controller by default! You must install one.*

• Ingress (The Object): The YAML file (The Rulebook) that you give to the Controller. It contains the instructions: "Route /login to the Auth Service."

5. Enabling Ingress in Minikube #

minikube addons enable ingress

*(Minikube will download and launch the NGINX controller Pods in the ingress-nginx namespace).*

6. Anatomy of an Ingress YAML #

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: main-ingress
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target: /
spec:
  rules:
  - host: myapp.com
    http:
      paths:
      - path: /api
        pathType: Prefix
        backend:
          service:
            name: api-service
            port:
              number: 3000

7. Mini Project: Path-Based Routing #

Step-by-Step Tutorial:

1. 1. Ensure the Ingress addon is enabled (Section 5).

1. 2. We need two services. Let's launch a "Blue" app and a "Red" app using imperative commands for speed:

kubectl create deployment blue-app --image=hashicorp/http-echo --args="-text=BLUE-APP"
kubectl expose deployment blue-app --port=80 --target-port=5678
kubectl create deployment red-app --image=hashicorp/http-echo --args="-text=RED-APP"
kubectl expose deployment red-app --port=80 --target-port=5678

1. 3. Create an ingress.yaml file to route the traffic:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: color-ingress
spec:
  rules:
  - http:
      paths:
      - path: /blue
        pathType: Prefix
        backend:
          service:
            name: blue-app
            port:
              number: 80
      - path: /red
        pathType: Prefix
        backend:
          service:
            name: red-app
            port:
              number: 80

1. 4. Apply it: kubectl apply -f ingress.yaml

1. 5. Test it: Ask Minikube for the IP address of the Ingress Controller: minikube ip. (Let's assume it returns 192.168.49.2).

1. 6. Open your browser to http://192.168.49.2/blue. You will see "BLUE-APP". Change the URL to /red and you will see "RED-APP". One IP address gracefully routing to two entirely different microservices!

8. Real-World Scenarios #

9. Best Practices #

• Host-Based Routing: In the real world, you rarely use raw IPs. You use host routing. You can configure your Ingress so that blog.company.com routes to the WordPress service, and app.company.com routes to the React service, all utilizing the exact same physical IP address.

10. Common Mistakes #

• Applying Ingress Rules Without a Controller: Beginners often write perfect ingress.yaml files, apply them, and then spend hours wondering why they get a "Page Not Found" error in the browser. The API Server accepts the Ingress rules perfectly, but if you forgot to install the actual NGINX Ingress Controller software into the cluster, there is no "receptionist" to actually enforce the rules!

11. Exercises #

1. 1. What is the fundamental financial and architectural advantage of utilizing a single Ingress Controller over deploying 20 Cloud LoadBalancer services?

1. 2. Differentiate between an "Ingress" (the Kubernetes object) and an "Ingress Controller".

12. FAQs #

13. Interview Questions #

• Q: Explain the concept of SSL Termination. How does an Ingress Controller facilitate SSL Termination within a Kubernetes microservice architecture?

• Q: A developer has successfully applied an Ingress manifest defining path-based routing (/api to api-service and /web to web-service). However, all external traffic is returning a generic 404 error from NGINX. Describe the architectural checks you would perform to debug this routing failure.

14. Summary #

15. Next Chapter Recommendation #