Running WSGI Apps with aiohttp

The aiohttp library in Python provides great support for asynchronous HTTP handling. However, many Python web applications are written using the WSGI standard interface. Thankfully, aiohttp provides a way to run WSGI apps directly, making it easy to leverage aiohttp's performance while still supporting existing WSGI apps.

Why Run WSGI in aiohttp?

There are a few key reasons you may want to run WSGI apps with aiohttp:

How the aiohttp WSGI Hosting Works

Under the hood, aiohttp implements a WSGI handler using a threadpool. Each WSGI request is handled in a separate thread using a thread pool executor. This allows the WSGI app to perform blocking I/O without impacting overall server performance.

Here is a simple example:

from aiohttp import web
import aiohttp_wsgi

def wsgi_app(environ, start_response):
  #...
  start_response('200 OK', [('Content-Type', 'text/plain')]) 
  return [b'Hello World']

app = web.Application()
app.router.add_route("*", "/{path_info:.*}", aiohttp_wsgi.WSGIHandler(wsgi_app))
web.run_app(app)

This mounts the WSGI app at the path /{path_info:.*}, handling all requests with the app.

Considerations for WSGI in aiohttp

There are a few things to keep in mind:

Overall though, for many workloads hosting WSGI in aiohttp provides an excellent performance boost. Care should be taken with expensive blocking I/O calls inside WSGI apps.