Kubernetes Level 02 Day 08: Deploy Tomcat App on Kubernetes

This document outlines the solution for Kubernetes Level 02 Day 08. The objective was to deploy a Java-based Tomcat application within a dedicated namespace and expose it via a NodePort service.

Table of Contents

1. Task Overview
2. Step-by-Step Solution
   • 1. Create the Namespace
   • 2. Define the Manifests
   • 3. Apply the Configuration
   • 4. Verification
3. Deep Dive: Tomcat on Kubernetes

---

Task Overview

Objective: Provision a Tomcat application stack in the tomcat-namespace-xfusion namespace.

• Namespace: tomcat-namespace-xfusion
• Deployment:
  • Name: tomcat-deployment-xfusion
  • Replicas: 1
  • Container Name: tomcat-container-xfusion
  • Image: gcr.io/kodekloud/centos-ssh-enabled:tomcat
  • Container Port: 8080
• Service:
  • Name: tomcat-service-xfusion
  • Type: NodePort
  • NodePort: 32227

---

Step-by-Step Solution

1. Create the Namespace

Start by isolating the Tomcat application resources.

Command:

kubectl create namespace tomcat-namespace-xfusion

2. Define the Manifests

Create a single YAML file containing both the Deployment and the Service configurations. Using a shared label like app: tomcat-app will link the service to the deployment.

Command:

vi tomcat-setup.yaml

Content:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: tomcat-deployment-xfusion
  namespace: tomcat-namespace-xfusion
spec:
  replicas: 1
  selector:
    matchLabels:
      app: tomcat-app
  template:
    metadata:
      labels:
        app: tomcat-app
    spec:
      containers:
      - name: tomcat-container-xfusion
        image: gcr.io/kodekloud/centos-ssh-enabled:tomcat
        ports:
        - containerPort: 8080
---
apiVersion: v1
kind: Service
metadata:
  name: tomcat-service-xfusion
  namespace: tomcat-namespace-xfusion
spec:
  type: NodePort
  selector:
    app: tomcat-app
  ports:
    - port: 8080
      targetPort: 8080
      nodePort: 32227

3. Apply the Configuration

Apply the declarative configuration to the cluster.

Command:

kubectl apply -f tomcat-setup.yaml

* Output:

deployment.apps/tomcat-deployment-xfusion created
service/tomcat-service-xfusion created

4. Verification

Ensure the pod is running and the service is correctly routing traffic.

Check Pod Status:

kubectl get pods -n tomcat-namespace-xfusion

Wait until the pod shows 1/1 under the READY column and status is Running.

Check Service Details:

kubectl get svc -n tomcat-namespace-xfusion

Verify that tomcat-service-xfusion maps port 8080:32227/TCP.

Access the UI: Once the pod is ready, open the provided browser or web view. Access the application via the Node's IP address on port 32227 (e.g., http://<node-ip>:32227). You should see the default Tomcat manager or welcome page.

---

Deep Dive: Tomcat on Kubernetes

The Container Image

The image used (gcr.io/kodekloud/centos-ssh-enabled:tomcat) is a specialized CentOS-based image with Tomcat pre-installed and SSH enabled. In a standard production environment, you would typically use an official slim image like tomcat:9-jre11-openjdk-slim to reduce the attack surface and image size.

Label Matchmaking

The selector block in the Service is the "glue" of Kubernetes networking. * Service Selector: app: tomcat-app * Deployment Pod Template Label: app: tomcat-app If these do not match exactly, the Service will have no endpoints and will fail to route traffic to your application, resulting in "Connection Refused" or "Timeout" errors.

NodePort Selection

By default, Kubernetes NodePorts are assigned from the 30000-32767 range. This task specified a precise port (32227), which is a common requirement when integrating with external firewalls or legacy load balancers that expect traffic on specific ports.