Does Flask Work With Docker?
Flask and Docker work together seamlessly, making it trivial to containerize Python web applications for consistent development, testing, and production deployments.
Quick Facts
How Flask Works With Docker
Flask is a lightweight WSGI framework that containerizes exceptionally well with Docker. You create a Dockerfile that specifies a Python base image, installs Flask and dependencies via pip, and runs the Flask application—typically behind a production WSGI server like Gunicorn. Docker's layering system means your Flask app builds quickly after initial setup, and the resulting image is compact (often under 100MB). The developer experience is straightforward: write your Flask app normally, define dependencies in requirements.txt, create a minimal Dockerfile, and run `docker build` and `docker run`. Flask's simplicity means there are no framework-specific gotchas with Docker—the integration is just standard containerization practices. This combo shines for microservices architectures where each Flask service runs in its own container, orchestrated by tools like Docker Compose or Kubernetes. Port mapping is handled naturally through Docker's `-p` flag, and environment configuration works well with Docker's env var support.
Best Use Cases
Quick Setup
pip install flask gunicorn# Dockerfile
FROM python:3.11-slim
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
EXPOSE 5000
CMD ["gunicorn", "--bind", "0.0.0.0:5000", "app:app"]
# app.py
from flask import Flask
app = Flask(__name__)
@app.route('/')
def hello():
return {'message': 'Hello from Docker!'}
if __name__ == '__main__':
app.run()
# requirements.txt
Flask==3.0.0
Gunicorn==21.2.0
# Build and run
# docker build -t flask-app .
# docker run -p 5000:5000 flask-appKnown Issues & Gotchas
Flask development server binding to localhost by default, making it unreachable from outside the container
Fix: Set `app.run(host='0.0.0.0')` or use the `FLASK_ENV` variable, or better yet, use Gunicorn in production containers
Large Docker images due to including development dependencies and unnecessary files in the context
Fix: Use multi-stage builds to separate build dependencies from runtime, and create a .dockerignore file to exclude __pycache__, .git, .venv, etc.
Database connection failures when using localhost in connection strings inside containers
Fix: Use service names (defined in docker-compose) or Docker's internal DNS, not localhost, for inter-container communication
Hot-reloading doesn't work in containers by default because file changes aren't reflected
Fix: Mount source code as a volume with `-v` flag or in docker-compose to enable live reloading during development
Alternatives
- •Django with Docker: More batteries-included Python framework, heavier but better for large monolithic apps
- •FastAPI with Docker: Modern async Python framework with better performance, ideal for high-concurrency APIs
- •Node.js Express with Docker: JavaScript alternative with similar lightweight philosophy, useful for polyglot teams
Resources
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