# Task Manager - Docker Web Application

A simple task manager web application deployed as a multi-container Docker system. Users can create, complete, and delete tasks through a web interface.

## Prerequisites

- **Linux** with Docker installed (Docker Engine 20.10+)
- **Docker Compose** v2 (optional, for `docker compose` deployment)
- Ports **80** must be available on the host machine

## Application Description

The Task Manager is a web-based CRUD application for managing personal tasks. It consists of three services working together:

- A **frontend** web interface served by Nginx where users interact with the application
- A **backend** REST API built with Flask (Python) that handles business logic
- A **PostgreSQL database** that stores task data persistently

Users can:
- Add new tasks
- Mark tasks as completed (toggle checkbox)
- Delete tasks
- View all tasks in a list sorted by creation date

## Architecture

```
Browser (port 80)
    |
    v
+--------+       +-------+       +------------+
| Nginx  | ----> | Flask | ----> | PostgreSQL |
| :80    |  API  | :5000 |  SQL  | :5432      |
+--------+ proxy +-------+       +------------+
  static           REST API        persistent
  files            (gunicorn)      volume
```

## Virtual Networks

| Network Name      | Driver | Purpose                                              |
|-------------------|--------|------------------------------------------------------|
| taskapp-network   | bridge | Connects all 3 containers so they can communicate    |

All containers are attached to `taskapp-network`. Only Nginx exposes a port (80) to the host. Flask and PostgreSQL are accessible only within the Docker network.

## Named Volumes

| Volume Name    | Mount Point                        | Purpose                          |
|----------------|------------------------------------|----------------------------------|
| taskapp-pgdata | /var/lib/postgresql/data (in db)   | Persists database data across container restarts and stops |

Stopping and restarting the application preserves all task data thanks to this volume.

## Containers

### 1. taskapp-nginx (Frontend)

- **Image:** Custom, built from `nginx:alpine`
- **Port:** 80 (host) -> 80 (container)
- **Role:** Serves static HTML/CSS/JS files and reverse-proxies `/api/*` requests to the Flask backend
- **Restart policy:** `unless-stopped`
- **Configuration:** Custom `nginx.conf` with `proxy_pass` directive for API routing and `large_client_header_buffers 4 32k` for handling large cookies

### 2. taskapp-flask (Backend)

- **Image:** Custom, built from `python:3.12-slim`
- **Port:** 5000 (internal only, not exposed to host)
- **Role:** REST API server handling task CRUD operations
- **Restart policy:** `unless-stopped`
- **Configuration:** Environment variables for database connection (`DB_HOST`, `DB_NAME`, `DB_USER`, `DB_PASSWORD`)
- **WSGI server:** Gunicorn with 2 workers
- **Auto-initialization:** Creates the `tasks` table on startup if it does not exist

### 3. taskapp-db (Database)

- **Image:** `postgres:15` (from Docker Hub)
- **Port:** 5432 (internal only, not exposed to host)
- **Role:** Stores task data (id, title, completed status, creation timestamp)
- **Restart policy:** `unless-stopped`
- **Configuration:** Environment variables (`POSTGRES_DB`, `POSTGRES_USER`, `POSTGRES_PASSWORD`)
- **Volume:** `taskapp-pgdata` mounted at `/var/lib/postgresql/data`

## Container Configuration Details

- **Nginx** is configured via `frontend/nginx.conf` which sets up static file serving and reverse proxy rules
- **Flask** reads database credentials from environment variables passed at container runtime
- **PostgreSQL** is configured via standard Postgres environment variables; data is stored on a named volume

## Usage Instructions

### Prepare the Application

Build images and create Docker resources:

```bash
./prepare-app.sh
```

### Start the Application

Run all containers:

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

Output:
```
Starting app...
App is running!
The app is available at http://localhost:80
```

### View in Web Browser

Open your web browser and navigate to:

```
http://localhost:80
```

You will see the Task Manager interface where you can add, complete, and delete tasks.

### Stop the Application

Stop all containers (data is preserved):

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

### Remove the Application

Remove all containers, images, networks, and volumes:

```bash
./remove-app.sh
```

### Alternative: Docker Compose

You can also use Docker Compose instead of the shell scripts:

```bash
# Start
docker compose up -d --build

# Stop (preserves data)
docker compose down

# Remove everything including volumes
docker compose down -v --rmi all
```

## API Endpoints

| Method | Endpoint          | Description            |
|--------|-------------------|------------------------|
| GET    | /api/tasks        | List all tasks         |
| POST   | /api/tasks        | Create a new task      |
| PUT    | /api/tasks/:id    | Toggle task completion |
| DELETE | /api/tasks/:id    | Delete a task          |

## Project Structure

```
.
├── backend/
│   ├── Dockerfile          # Python/Flask image definition
│   ├── requirements.txt    # Python dependencies
│   └── app.py              # Flask REST API application
├── frontend/
│   ├── Dockerfile          # Nginx image definition
│   ├── nginx.conf          # Nginx configuration (static files + reverse proxy)
│   ├── index.html          # Main HTML page
│   ├── style.css           # Styles
│   └── app.js              # Frontend JavaScript (fetch API calls)
├── docker-compose.yaml     # Docker Compose configuration
├── prepare-app.sh          # Script to build images and create resources
├── start-app.sh            # Script to start all containers
├── stop-app.sh             # Script to stop all containers
├── remove-app.sh           # Script to remove all traces of the app
└── README.md               # This file
```

## Example of Working with the Application

```bash
# Prepare everything needed for the application
./prepare-app.sh
# Output:
# Preparing app...
# Building backend image...
# Building frontend image...
# Creating network...
# Creating volume...
# App prepared successfully.

# Start the application
./start-app.sh
# Output:
# Starting app...
# Starting database...
# Starting backend...
# Starting frontend...
#
# App is running!
# The app is available at http://localhost:80

# Open web browser and work with the application at http://localhost:80
# - Add tasks using the input field
# - Mark tasks as completed by clicking the checkbox
# - Delete tasks by clicking the X button

# Stop the application (data is preserved)
./stop-app.sh
# Output:
# Stopping app...
# App stopped.

# Start again - all tasks are still there
./start-app.sh

# Remove everything related to the application
./remove-app.sh
# Output:
# Removing app...
# App removed.
```

## Sources

- [Docker Documentation](https://docs.docker.com/)
- [Nginx Docker Image](https://hub.docker.com/_/nginx)
- [PostgreSQL Docker Image](https://hub.docker.com/_/postgres)
- [Python Docker Image](https://hub.docker.com/_/python)
- [Flask Documentation](https://flask.palletsprojects.com/)
- [Gunicorn Documentation](https://gunicorn.org/)
- [Nginx Reverse Proxy Guide](https://docs.nginx.com/nginx/admin-guide/web-server/reverse-proxy/)

## Use of Artificial Intelligence

This application was designed and implemented with the assistance of **Claude** (Anthropic), an AI assistant. Claude was used for:

- Designing the application architecture and service composition
- Writing application source code (Python/Flask backend, HTML/CSS/JS frontend)
- Writing Dockerfiles and Docker Compose configuration
- Writing shell scripts for application lifecycle management
- Writing this documentation

**AI agent used:** Claude Opus 4.6 (Anthropic) via Claude Code CLI