Giles Thomas - An HTTP request's journey through a platform-as-a-service PythonAnywhere hosts tens of thousands of Python web applications, with traffic ranging from a couple of hits a week to dozens of hits a second. Hosting this many sites reliably at a reasonable cost requires a well-designed infrastructure, but it uses the same standard components as many other Python-based websites. We've built our stack on GNU/Linux, nginx, uWSGI, Redis, and Lua -- all managed with Python. In this talk we'll give a high-level overview of how it all works, by tracing how a request goes from the browser to the Python application and its response goes back again. As well as showing how a fairly large deployment works, we'll give tips on scaling and share a few insights that may help people running smaller sites discover how they can speed things up.