Battleship Application on Kubernetes

Overview

This application implements a Battleship game system composed of three main components:

The application is deployed in a Kubernetes cluster using Deployments, a StatefulSet with persistent storage, and Services for network exposure.

battleship-backend:
- Description: Contains the backend logic for the game.
- Port: Listens on port 4000.
- Configuration: Uses environment variables to connect to the MySQL database.
battleship-frontend:
- Description: Hosts the web user interface for the game.
- Port: Listens on port 80.
- Exposure: Exposed via a NodePort (30001).
MySQL (battleship-mysql):
- Description: Runs a MySQL database (version 8.0.30) in a StatefulSet.
- Port: Uses port 3306.
- Persistence: Uses a PersistentVolume (PV) and PersistentVolumeClaim (PVC) for data storage.

Namespace:
- battleship-app
  All objects (Deployments, StatefulSet, Services, PV, PVC) are created within this namespace.
Deployments:
- battleship-backend: Manages the backend pods.
- battleship-frontend: Manages the frontend pods.
StatefulSet:
- battleship-mysql: Manages the MySQL pods with stable identities and persistent storage. It includes:
  - PersistentVolume (mysql-pv): Provides 1Gi storage (using a hostPath at /mnt/data/mysql).
  - PersistentVolumeClaim (mysql-pvc): Claims the persistent storage for MySQL.
Services:
- MySQL Service: Exposes the MySQL StatefulSet on port 3306.
- Backend Service: Exposes the backend on port 4000 (via NodePort 30000).
- Frontend Service: Exposes the frontend on port 80 (via NodePort 30001).

Virtual Networks:
Kubernetes provides internal networking for the cluster, and Services offer stable endpoints for communication between pods.
Note: In the original Docker Compose configuration, a network named app-net was defined; in Kubernetes, the cluster’s internal network is used.
Named Volumes:
The MySQL StatefulSet uses a PersistentVolume and a PersistentVolumeClaim to ensure data persistence. This setup guarantees that data (e.g., the game database) survives pod restarts or rescheduling.

Environment Variables:
- Backend Container:
  Configured with variables such as DB_HOST, DB_PORT, DB_USER, DB_PASSWORD, and DB_NAME to connect to the MySQL database.
- MySQL Container:
  Configured with variables MYSQL_ROOT_PASSWORD and MYSQL_DATABASE to initialize the database.
Ports:
- Backend: Container port 4000, exposed on NodePort 30000.
- Frontend: Container port 80, exposed on NodePort 30001.
- MySQL: Container port 3306, exposed internally on port 3306.
Image Pull Policy:
The backend and frontend Deployments use imagePullPolicy: Never assuming images are built locally.

Build Docker Images:
Execute the prepare-app.sh script to build the Docker images for the backend and frontend:
```
./prepare-app.sh
```

Deploy the Application:
Use the start-app.sh script to deploy the namespace, Deployments, StatefulSet, and Services:
```
./start-app.sh
```

Scale Down the Application:
If you need to temporarily pause the application without deleting objects (thus preserving the data), use:
```
./stop-app.sh
```
Note: This script scales the Deployments and StatefulSet to 0 replicas.

Delete All Kubernetes Objects:
To completely remove the application—including Deployments, StatefulSet, Services, and the Namespace—execute:
```
./remove-app.sh
```
Important: Deleting the objects may also remove the associated PersistentVolume depending on its reclaim policy. To preserve data, consider setting the PersistentVolume's reclaim policy to Retain.

Frontend Access:
The frontend is exposed via a NodePort on port 30001.
Open a web browser and navigate to:
```
http://<Node-IP>:30001
```
Replace <Node-IP> with the IP address of one of your Kubernetes nodes.