PHP at Scale: Knowing enough to be dangerous! by Oleksii Petrov discusses how to scale PHP applications. It covers strategies like caching, queueing, read/write splitting, and sharding. It also discusses using load balancers and choosing the right database. The key is to improve system metrics without dramatically changing the system. Scaling is predefined by your stack and architecture. Performance comes from optimizations everywhere, not just PHP. Being distributed is very challenging.