Day 5: Deployment with Gunicorn and Docker

Today's Objective

Production Flask: Gunicorn workers, Nginx reverse proxy, environment variables, Docker containers, and the minimal CI/CD pipeline that ships code safely.

Building a JSON API

API views

from flask import jsonify @app.route('/api/posts', methods=['GET']) def api_posts(): posts = Post.query.filter_by(published=True).all() return jsonify([{'id': p.id, 'title': p.title, 'body': p.body} for p in posts]) @app.route('/api/posts/', methods=['GET']) def api_post(id): post = Post.query.get_or_404(id) return jsonify({'id': post.id, 'title': post.title, 'body': post.body}) @app.route('/api/posts', methods=['POST']) @login_required def api_create_post(): data = request.get_json() if not data or not data.get('title'): return jsonify({'error': 'title required'}), 400 post = Post(title=data['title'], body=data.get('body',''), user_id=current_user.id) db.session.add(post) db.session.commit() return jsonify({'id': post.id}), 201

CORS

pip install flask-cors

from flask_cors import CORS
CORS(app, resources={r'/api/*': {'origins': 'https://yourfrontend.com'}})

Deploy to Render

# render.com → New Web Service → Connect GitHub
# Build command: pip install -r requirements.txt
# Start command: gunicorn app:app
# Add env vars: SECRET_KEY, DATABASE_URL

# requirements.txt
flask
flask-sqlalchemy
flask-migrate
gunicorn
psycopg2-binary
dj-database-url

📝 Day 5 Exercise

Deploy Your Flask App

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Day 5 Summary

jsonify() converts Python dicts/lists to JSON responses with the correct Content-Type header.
Return proper status codes: 200 OK, 201 Created, 400 Bad Request, 404 Not Found, 401 Unauthorized.
Flask-CORS adds CORS headers. Restrict origins to your frontend domain in production.
gunicorn is the production WSGI server. gunicorn app:app = filename:flask_instance.

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Day 4: Authentication

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Course Complete

Completing all five days means having a solid working knowledge of Flask in 5 Days. The skills here translate directly to real projects. The next step is practice — pick a project and build something with what was learned.

Supporting Videos & Reading

Go deeper with these external references.

YouTube

Deployment with Gunicorn and Docker — Video Walkthroughs Community tutorials and walkthroughs covering the concepts in this lesson.

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YouTube

Deployment with Gunicorn and Docker Explained Deep-dive explanations and live-coding sessions from top educators.

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Official Docs

Official Documentation Primary reference documentation for the technologies covered in this lesson.

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GitHub

Open Source Examples Real-world codebases demonstrating the patterns taught in this lesson.

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Day 5 Checkpoint

Before moving on, verify you can answer these without looking:

What is the core concept introduced in this lesson, and why does it matter?
What are the two or three most common mistakes practitioners make with this topic?
Can you explain the key code pattern from this lesson to a colleague in plain language?
What would break first if you skipped the safeguards or best practices described here?
How does today's topic connect to what comes in Day the final lesson?

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