The document discusses extending Nginx functionalities with Lua. It provides an overview of Nginx architecture and how the lua-nginx-module allows running Lua scripts inside Nginx. This provides a powerful and performant programming environment while taking advantage of Nginx's event-driven architecture. Examples show how to access Nginx variables and APIs from Lua, issue subrequests, and do non-blocking I/O including with cosockets. Libraries like lua-resty-memcached reuse these extensions. In summary, Nginx is excellent for scalable apps and Lua extends its capabilities through embedded scripts and subrequests.