Understanding Kubernetes Through a Simple Todo App

March 26, 2025

Introduction

In this guide, we’ll explore how to deploy a simple Todo application on Kubernetes. We’ll focus on understanding Kubernetes components and how they work together to run our application.

Source Code

All code for this tutorial is available on GitHub:

git clone https://github.com/akamasine/Demo-Todo.git

What We’re Building

A 3-tier Todo application consisting of:

• Frontend: React application
• Backend: Node.js/Express API
• Database: PostgreSQL

Understanding Kubernetes Components

1. Database Layer

Our PostgreSQL database is managed through:

• ConfigMap: Stores database configuration
• Secret: Securely stores database password
• PersistentVolume: Provides persistent storage
• Service: Enables internal communication

Think of this layer as a secure filing cabinet that:

• Keeps data safe and persistent
• Is accessible only within the cluster
• Maintains configuration separately from code

2. Backend Layer

The Node.js API is managed by:

• Deployment: Runs and manages API pods
• Service: Routes internal traffic
• Uses ConfigMap and Secret for database connection

This layer acts like a data processor that:

• Handles API requests
• Communicates with the database
• Can scale based on demand

3. Frontend Layer

The React frontend is managed through:

• Deployment: Runs the web interface
• Service: Manages pod access
• Ingress: Handles external access

Think of this as the user interface that:

• Presents the Todo application
• Communicates with the backend
• Is accessible from outside the cluster

How It All Works Together

1. User Interaction Flow

When a user interacts with the application:

1. Request hits the Ingress
2. Ingress routes to appropriate service
3. Service directs to correct pod
4. Pod processes the request

2. Data Flow

For creating a todo:

1. User enters todo item
2. Frontend sends request through Ingress
3. Backend pod receives request
4. Backend connects to database
5. Data is stored persistently

Common Kubernetes Patterns Used

1. Configuration Management

• ConfigMaps for non-sensitive settings
• Secrets for sensitive data
• Environment variables injection

2. Service Discovery

• Internal DNS resolution
• Service abstraction
• Pod-to-pod communication

3. State Management

• Persistent storage for database
• Stateless application pods
• Data persistence across restarts

Getting Started

1. Prerequisites:
   • Minikube installed
   • kubectl configured
   • Docker installed
2. Clone the repository:

   git clone https://github.com/akamasine/Demo-Todo.git
   

3. Follow the setup instructions in the repository’s README.md

Key Takeaways

1. Separation of Concerns
   • Each component has specific responsibilities
   • Configuration separate from code
   • Clear boundaries between services
2. Kubernetes Benefits
   • Declarative configuration
   • Automatic scaling
   • Self-healing capabilities
   • Easy service discovery
3. Best Practices
   • Use appropriate resource types
   • Implement proper health checks
   • Maintain security with Secrets
   • Keep configurations separate

Conclusion

This Todo application demonstrates fundamental Kubernetes concepts in a practical way. While simple, it showcases patterns used in larger applications.

Next Steps

• Add authentication
• Implement monitoring
• Set up CI/CD pipeline
• Add database replication

Resources

• Project Repository
• Kubernetes Documentation
• Minikube Documentation