Stack Overflow Architecture

Stack Overflow launched in 2008 and has a code base that is 14 years old. It run on prem, we run on our own data center, we haven't gone to the cloud. We also have a monolithic application, so we have not breaking down into services or microservices. And we have a multi-tenant web app running on a single app pool across nine web servers only. That same application, single app pool on IIS, is handling 6,000 requests per second at the moment.