An Internal Developer Platform (IDP) is essential for rapidly scaling companies to keep developers working productively and happily. Jason Warner, CTO of GitHub and former VP of Engineering at Heroku, shares his experience on building an IDP to solve scalability issues and improve development workflows. Initially, GitHub was built on bash scripts that didn't scale, but as the company grew, they needed a more efficient setup. The team decided to base their IDP on Kubernetes and created a bespoke platform with specialized teams for managing services, containers, and packages. Rolling out the IDP improved scalability, reduced headcount in ops, and increased developer productivity. However, Jason learned that building an IDP is not a straightforward process and requires significant investment. He advises companies to use GitHub and Heroku as a starting point and only build an IDP if their setup exceeds a certain threshold of complexity.