WSGI is a great standard. It has been amazingly successful. In order to describe how successful it is, let me describe life before WSGI. In the beginning, CGI existed. CGI was just a standard for how a web server can run a process — what environment variables to pass, and so forth. In order to write a web-based application, people would write programs that complied with CGI. At that time, Apache’s only competition was commercial web servers, and CGI allowed you to write applications that ran on both. However, starting a process for each request was slow and wasteful.
For Python applications, people wrote mod_python for Apache. It allowed people to write Python programs that ran inside the Apache process, and directly used Apache’s API to access the HTTP request details. Since Apache was the only server that mattered, that was fine. However, as more servers arrived, a standard was needed. mod_wsgi was originally a way to run the same Django application on many servers. However, as a side effect, it also allowed the second wave of Python web application frameworks –Paste, Flask and more — to have something to run on. In order to make life easier, Python included wsgiref, a module that implemented a single-thread single-process blocking web server with the WSGI protocol.
Some web frameworks come with their own development web servers that will run their WSGI apps. Some use wsgiref. Almost always those options are carefully documented as “just for development use, do not use in production.” Wouldn’t it be nice to use the same WSGI container in both development and production, eliminating one potential source of reproduction bugs?
For ease of use, it should probably be written in Python. Luckily, “twist web –wsgi” is just such a server. In order to show-case how easy it is to use it, twist-wsgi shows commands to run Django, Flask, Pyramid and Bottle apps as easy as it is to run frameworks’ built-in web server.
In production, using the Twisted WSGI containers come with several advantages. Production-grade SSL support using PyOpenssl and cryptography allows elimination of “SSL terminators”, removing one moving piece from the equation. With third-party extensions like txsni and txacme, it allows modern support for “easy SSL”. The built-in HTTP/2 support, starting with Twisted 16.3, allows better support for parallel requests from modern browsers.
The Twisted web server also has a built-in static file server, allowing the elimination of a “front-end” web server that deals with static files by itself, and passing dynamic requests to the application server.
Twisted is also not limited to web serving. As a full-stack network application, it has support for scheduling repeated tasks, running processes and supporting other protocols (for example, a side-channel for online control). Last but not least, in order to integrate that, the language used is Python. As an example for an integrated solution, the Frankenstenian monster plugin show-cases a combo web application combining 4 frameworks, a static file server and a scheduled task updating a file.
While the goal is not to encourage using four web frameworks and a couple of side services in order to greet the user and tell them what time it is, it is nice that if the need strikes this can all be integrated into one process in one language, without the need to remember how to spell “every 4 seconds” in cron or how to quote a string in the nginx configuration file.