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Kubernetes Level 02 Day 09: Deploy Node App on Kubernetes

This document outlines the solution for Kubernetes Level 02 Day 09. The objective was to deploy a Node.js application using a Deployment with multiple replicas and expose it through a NodePort service on a specific port.

Table of Contents

  1. Task Overview
  2. Step-by-Step Solution
  3. Deep Dive: NodePort and TargetPort

Task Overview

Objective: Provision a Node.js application stack and ensure it is accessible via the NodeApp interface.

  • Deployment:
    • Name: node-app-deployment (Choice)
    • Image: gcr.io/kodekloud/centos-ssh-enabled:node
    • Replicas: 2
    • Container Name: node-container (Choice)
  • Service:
    • Name: node-app-service (Choice)
    • Type: NodePort
    • TargetPort: 8080
    • NodePort: 30012

Step-by-Step Solution

1. Create the Unified Manifest File

We will create a YAML file that defines both the Deployment and the Service. This ensures consistency between the pod labels and the service selector.

Command: 

vi node-app.yaml

Content: 

apiVersion: apps/v1
kind: Deployment
metadata:
  name: node-app-deployment
  labels:
    app: node-app
spec:
  replicas: 2
  selector:
    matchLabels:
      app: node-app
  template:
    metadata:
      labels:
        app: node-app
    spec:
      containers:
      - name: node-container
        image: gcr.io/kodekloud/centos-ssh-enabled:node
        ports:
        - containerPort: 8080
---
apiVersion: v1
kind: Service
metadata:
  name: node-app-service
spec:
  type: NodePort
  selector:
    app: node-app
  ports:
    - port: 80
      targetPort: 8080
      nodePort: 30012

2. Apply the Configuration

Apply the manifest using kubectl.

Command: 

kubectl apply -f node-app.yaml
* Output: 
deployment.apps/node-app-deployment created
service/node-app-service created

3. Verification

Ensure that the pods are running and the service is correctly routing traffic.

Check Pod Status: 

kubectl get pods
Wait until both pods show 1/1 under READY and status is Running.

Check Service Details: 

kubectl get svc node-app-service
Verify the mapping shows 80:30012/TCP.

Access the UI: Once verified, click the NodeApp button on the top bar of the lab environment. You should see the response from the Node.js application.

Deep Dive: NodePort and TargetPort

Port Configuration Explained

In this task, we managed three different port levels: 1. ContainerPort (8080): The port the Node.js application is listening on inside the container. 2. TargetPort (8080): The port on the pod that the Service sends traffic to. This must match the port used by the application in the container. 3. Port (80): The internal cluster port for the service. Other pods in the cluster can access this app via http://node-app-service:80. 4. NodePort (30012): The port opened on every node's IP address. This allows external access via http://<NodeIP>:30012.

High Availability

By setting replicas: 2, Kubernetes ensures that two instances of the application are running across the cluster. If one pod fails or a node goes down, the Deployment controller will automatically spin up a new instance to maintain the desired state of 2 replicas.