Design YouTube, then implement the cache layer.

When designing YouTube, focus on the core features such as video uploading, streaming, user accounts, and recommendations. Consider the user experience and scalability as you outline the architecture. For the cache layer implementation, discuss specific caching strategies (e.g., CDN, in-memory caching) and how they would optimize video delivery and reduce latency. Be prepared to explain how you would manage cache invalidation and handle user-generated content efficiently. Highlight trade-offs between consistency and performance in your caching approach.