This document provides an overview of backend architectures and strategies for scaling web applications. It discusses choosing between scaling up (buying more powerful hardware) versus scaling out (adding more commodity servers). It recommends using caching, databases, cloud services, and other techniques like sharding, replication and indexing to improve performance and allow applications to handle increased load. Specific technologies mentioned include memcached, MongoDB, Redis, MySQL, and content delivery networks. The document emphasizes the importance of proper planning, monitoring, and avoiding premature optimization.