Achieve zero-downtime Flask deployments with graceful reloads: keep the current WSGI instance cached in memory so in‑flight and new requests are served during code updates, then seamlessly swap workers. Use Gunicorn with --reload and multiple --workers, plug into your CI/CD, and roll out production changes without interruptions.
Flask apps can slow as they grow; this guide shows how to find and fix bottlenecks. Use profiling (line_profiler) to measure line-by-line costs, then optimize: switch from the dev server to WSGI (Gunicorn/uWSGI), streamline routes and DB queries (eager loading, caching), cache and minify templates, and enable connection pooling. Continuous tuning boosts throughput, scalability, and user experience under heavy load.
Step-by-step guide to scaling a Flask app: create a virtualenv, install Flask and Gunicorn, write a basic app, then run it via gunicorn -w 4 --bind unix:/tmp/myapp.sock myapp:app to use multiple workers and a Unix socket; for production, put Gunicorn (or uWSGI) behind Nginx, proxying to /tmp/myapp.sock, enable the site, and reload Nginx for a robust, production-ready deployment.
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