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devop_note/uWSGI.md

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+---
+aliases:
+up: "[[00_devop_note]]"
+tags:
+  - devop
+---
+w
+# What is uWSGI?
+
+**uWSGI** is an application server that sits between a web server (like Nginx or Apache) and a Python web application (like Django, Flask, or FastAPI). It runs your Python code and handles incoming web requests.
+
+The name comes from **WSGI** (Web Server Gateway Interface), which is the standard Python spec (PEP 3333) that defines how web servers talk to Python applications. The lowercase "u" is the Greek letter μ (micro), suggesting it's lightweight — though in practice it grew into a full-featured server.
+
+## Why do we need it?
+
+A plain web server like Nginx doesn't know how to execute Python code. It only serves static files (HTML, CSS, images) and forwards dynamic requests elsewhere. You need a process that:
+
+1. Loads your Python application into memory
+2. Receives requests from the web server
+3. Calls your Python code with the request
+4. Returns the response back to the web server
+
+That middle process is uWSGI (or alternatives like Gunicorn).
+
+## The typical stack
+
+```
+Browser → Nginx → uWSGI → Python app (Django/Flask)
+```
+
+- **Nginx**: handles SSL, static files, load balancing, gzip, caching
+- **uWSGI**: runs Python workers, manages processes/threads
+- **Python app**: your business logic
+
+Nginx and uWSGI usually talk over a **Unix socket** (fast, local) or a TCP port. The protocol between them is called the **uwsgi protocol** (lowercase) — a binary protocol that's faster than plain HTTP.
+
+## Key features
+
+- **Process management**: spawns multiple worker processes to handle concurrent requests
+- **Threading**: each worker can run multiple threads
+- **Auto-reload**: restart workers when code changes (dev mode)
+- **Emperor mode**: one master process supervising many vassal apps
+- **Cheaper mode**: dynamically scale workers up/down based on load
+- **Multi-language**: despite the name, also supports Ruby, Perl, Go, etc.
+
+## Minimal config example
+
+A typical `uwsgi.ini`:
+
+```ini
+[uwsgi]
+module = myproject.wsgi:application
+master = true
+processes = 4
+threads = 2
+socket = /tmp/myproject.sock
+chmod-socket = 660
+vacuum = true
+die-on-term = true
+```
+
+- `module`: entry point (the WSGI callable)
+- `processes`: how many worker processes to fork
+- `socket`: where Nginx connects to
+- `vacuum`: clean up the socket on exit
+- `die-on-term`: shut down cleanly on SIGTERM
+
+## Running it
+
+```bash
+uwsgi --ini uwsgi.ini
+```
+
+Or in production, run it under **systemd** so it restarts on failure.
+
+## uWSGI vs Gunicorn
+
+Both are WSGI servers. The community has largely shifted toward **Gunicorn** because:
+
+- Simpler config
+- Fewer footguns
+- Easier to deploy
+
+uWSGI is more feature-rich and faster in some benchmarks, but its config surface is huge (hundreds of options) and the project has had governance/maintenance concerns. For new projects, Gunicorn behind Nginx is the common default.
+
+## When you'll see uWSGI
+
+- Legacy Django/Flask deployments
+- Setups that need uWSGI-specific features (Emperor, cheaper, etc.)
+- Docker images for older Python web apps
+
+## Related
+
+- [[Apache Tomcat]] — the Java equivalent role (servlet container running Java apps behind a web server)