Shopping List Web Application on Kubernetes

Overview

This project deploys a Python shopping list web application using Flask and PostgreSQL on a Kubernetes cluster. The application allows users to create, track, and manage their shopping items in a persistent way. The deployment includes a Namespace, Deployments for both the web application and PostgreSQL database, a StatefulSet (with PersistentVolume and PersistentVolumeClaim), and Service.

Application Description

• Simple shopping list application that allows users to add, mark as purchased, and delete items
• Each item can have a quantity associated with it
• All data is stored in PostgreSQL for persistence between application restarts
• The application uses a Flask web framework with a minimalist interface

Containers

• simple-web-app: Runs the Python Flask application on port 5000
• postgres: Runs PostgreSQL database to store shopping list items

Kubernetes Objects

• Namespace: Isolates all the resources under my-app
• Deployment (Web App): Manages the stateless web application pods with 2 replicas for high availability
• Deployment (PostgreSQL): Manages the PostgreSQL database with persistent storage
• StatefulSet: Manages stateful application pods that require persistent storage
• PersistentVolume (PV): Provides persistent storage from the host (1GB)
• PersistentVolumeClaim (PVC): Claims the PV for storage
• Service (Web App): Exposes the web application externally via LoadBalancer
• Service (PostgreSQL): Headless service for internal database access

Networking and Storage

• Internal service discovery allows the web application to connect to PostgreSQL
• PostgreSQL uses persistent storage to maintain shopping list data even if pods are restarted
• The web application is exposed externally using a LoadBalancer service

Container Configuration

• The web app container is based on Python and includes Flask and psycopg2
• PostgreSQL container uses the official PostgreSQL image
• Resource limits and readiness probes are configured for better stability

How to Prepare, Run, Pause, and Delete the Application

1. Prepare the application:

   ./prepare-app.sh
   

   This script builds the Docker image and creates the directory for persistent volume.

2. Start the application:

   ./start-app.sh
   

   This script creates all necessary Kubernetes objects in the correct order, including PostgreSQL.

3. Pause or delete the application:

   ./stop-app.sh
   

   This script removes all Kubernetes objects created by start-app.sh.

Accessing the Application

To access the application:

1. Find the IP address of your Kubernetes node:

   kubectl get nodes -o wide
   

2. Access the application in your browser at:

   http://<NODE_IP>:80
   

   Where <NODE_IP> is the IP address of any of your Kubernetes nodes.

Application Features

• Add items with quantity
• Mark items as purchased/unpurchased
• Delete items
• Items list is separated into "to buy" and "purchased" sections
• Data persists between sessions and application restarts

Database Schema

The application uses a simple PostgreSQL schema:

• Table: shopping_items
• Fields:
  • id: Serial primary key
  • item: Text (item name)
  • quantity: Integer (defaults to 1)
  • purchased: Boolean flag (defaults to false)

Troubleshooting

If you encounter issues:

1. Check pod status:

   kubectl get pods -n my-app
   

2. View pod logs:

   kubectl logs <pod-name> -n my-app
   

3. Check service status:

   kubectl get svc -n my-app
   

4. Check database connectivity:

   kubectl exec -it <web-app-pod-name> -n my-app -- python -c "import psycopg2; conn = psycopg2.connect(host='postgres', dbname='postgres', user='postgres', password='postgres'); print('Connection successful')"