# Notes App — Kubernetes Deployment

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

---

## 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

---

## 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 |

---

## 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 |

---

## 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

---

## 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

---

## How to use

### 1. Prepare (build image, create host directory)

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

### 2. Start the application

```bash
./start-app.sh
```

### 3. Open in browser

```bash
./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)

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

### 5. Delete everything

```bash
./stop-app.sh
```

---

## 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
```