This document discusses how to scale applications on DigitalOcean from a single server architecture to millions of users. It describes starting with a single application server and database, then adding components like caching and load balancing as traffic increases. Key steps include adding high memory droplets for caching, using block storage for persistent storage, tagging droplets, and load balancing multiple application servers. The document provides a demo and tips for monitoring, not scaling too quickly, and tracing everything.