The document discusses various techniques for scaling PHP applications, including: 1. Using load balancers to distribute traffic across multiple servers and ensure high availability. 2. Implementing session persistence to maintain user sessions as clients are load balanced. 3. Separating static and dynamic content to improve performance by serving static files from optimized servers. 4. Caching frequently accessed data and generated pages to reduce database queries. 5. Database replication and other techniques for scaling the application database infrastructure. 6. Code optimization methods like opcode caching and acceleration. 7. Design considerations like modularity when planning for scalability.