ZKT26/Z2/z2/README.md

Notes App — Kubernetes Deployment

A simple web application where you can write, view, and delete notes. Built with Flask (Python) and PostgreSQL.

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What the app does

• Add a note using the text box on the main page
• View all saved notes
• Delete any note with a button click
• Notes are stored in a PostgreSQL database and survive pod restarts

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Containers used

Container	Image	Description
notes-web	notes-web:latest (built locally)	Flask web app — serves the UI and handles requests
postgres	postgres:15-alpine	PostgreSQL database — stores notes

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Kubernetes objects

Object	Name	Description
Namespace	notes-app	Isolates all app objects from other workloads
Deployment	notes-web	Runs 2 replicas of the Flask web app
StatefulSet	postgres	Runs 1 PostgreSQL pod with stable identity
PersistentVolume	postgres-pv	1Gi volume backed by host path /mnt/notes-postgres-data
PersistentVolumeClaim	postgres-pvc	Claims the PV for use by the StatefulSet
Service (NodePort)	notes-web-service	Exposes the web app on port 30080
Service (ClusterIP)	postgres-service	Internal access to PostgreSQL for the web app
Service (Headless)	postgres-headless	Required by the StatefulSet for stable DNS

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Networking and volumes

Services:

• notes-web-service — NodePort, exposes port 30080 externally → routes to pod port 5000
• postgres-service — ClusterIP, internal only, port 5432 → the web app connects to this
• postgres-headless — Headless service (no ClusterIP) used by the StatefulSet

Volume:

• postgres-pv uses a hostPath at /mnt/notes-postgres-data on the node
• Data persists even if the PostgreSQL pod is restarted or recreated

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Container configuration

notes-web:

• Environment variables set the database connection: DB_HOST, DB_PORT, DB_NAME, DB_USER, DB_PASS
• imagePullPolicy: Never — uses the locally built image (no registry needed)
• Runs on port 5000

postgres:

• POSTGRES_DB, POSTGRES_USER, POSTGRES_PASSWORD configure the database on first start
• Data directory /var/lib/postgresql/data is mounted from the PVC

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How to use

1. Prepare (build image, create host directory)

chmod +x prepare-app.sh start-app.sh stop-app.sh show-url.sh
./prepare-app.sh

2. Start the application

./start-app.sh

3. Open in browser

./show-url.sh

Or open manually:

• Minikube: minikube service notes-web-service -n notes-app
• Other: http://<node-ip>:30080

4. Stop (keep objects, scale down)

kubectl scale deployment notes-web -n notes-app --replicas=0
kubectl scale statefulset postgres -n notes-app --replicas=0

5. Delete everything

./stop-app.sh

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File overview

z2/
├── app/
│   ├── app.py            # Flask application
│   ├── requirements.txt  # Python dependencies
│   └── Dockerfile        # Image definition for notes-web
├── namespace.yaml        # Namespace: notes-app
├── deployment.yaml       # Deployment: notes-web (Flask)
├── statefulset.yaml      # StatefulSet + PV + PVC (PostgreSQL)
├── service.yaml          # Services: notes-web-service, postgres-service
├── prepare-app.sh        # Build image, create host directory
├── start-app.sh          # Apply all Kubernetes objects
├── stop-app.sh           # Delete all Kubernetes objects
├── show-url.sh           # Print the URL to open the app
└── README.md             # This file