How DNS Actually Works: Resolution Hierarchy, Caching, and Production Failure Modes

DNS is often misunderstood as a static phonebook, but it's actually a dynamic indirection layer that separates human-readable identifiers from volatile IP addresses. This distinction has significant architectural implications for resilience and scalability. To avoid DNS-related issues, it's essential to understand TTL tuning and negative caching, and to plan accordingly for migrations and changes. Engineers should set TTLs to allow for propagation before making changes, rather than trying to rush the process. This requires a fundamental shift in thinking about DNS as a solved infrastructure problem.