You understand the basics, but building an image every time you change a line of code is too slow. In this guide, we will use the modern package manager uv to set up our project and Docker Compose to create a "mirror" between your computer and the container.
Step 1: The Setup (Crucial First Steps)
We need to generate the uv.lock file locally first. This file ensures that Docker installs the exact same versions of libraries that you have on your machine.
1. Run these commands
Run this in your terminal to initialize the project and generate the lockfile.
cd my-docker-app
# Initialize uv
uv init
# Add Flask (This creates uv.lock!)
uv add flask
2. Create app.py
Create this file manually. Note debug=True is required for auto-reload.
app = Flask(__name__)
@app.route('/')
def hello():
return 'Hello from Docker!'
if __name__ == '__main__':
app.run(host='0.0.0.0', port=5000, debug=True)
Checkpoint
Before moving to Step 2, look at your folder. Do you see a file named uv.lock? Docker needs this file to build successfully!
Step 2: The "Pure UV" Dockerfile
The Dockerfile
We copy the uv binary directly into our image. This allows us to install dependencies blazingly fast using the lockfile we generated in Step 1.
FROM python:3.12-slim
# 1. Install uv directly into the container
COPY --from=ghcr.io/astral-sh/uv:latest /uv /bin/uv
WORKDIR /app
# 2. Copy dependency files FIRST (for caching)
COPY pyproject.toml uv.lock* ./
RUN uv sync --frozen --no-install-project
# Copy your source code
COPY . .
RUN uv sync --frozen
# 4. Copy the rest of the code
COPY . .
CMD ["python", "main.py"]Don't forget .dockerignore
Since uv creates a local .venv folder, we must tell Docker to ignore it to keep the image small.
Create .dockerignore:
.venv/
__pycache__/
.git/
Step 3: The "Magic" Mirror (Volumes)
This is the configuration that connects VS Code to Docker. We use the volumes key to map your folder into the container.
Create a file named docker-compose.yml:
services:
web-server:
build: .
ports:
- "8080:5000"
volumes:
- .:/app # <--- The Magic Link
Step 4: Control & Shell Access
Your environment is ready. Here is how you control it.
| Goal | Command |
|---|---|
| Start (With Hot Reload) Code changes apply instantly |
docker-compose up -d |
|
Enter the Shell
Open a terminal inside the running container |
docker-compose exec web-server bash
Once inside, you are in Linux!
Type ls to see files, or exit to leave.
|
| View Logs See Python print statements |
docker-compose logs -f |
| Stop Everything | docker-compose down |
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