3.1.2. Implementing Scalability Patterns

Your application works perfectly with 100 users. What happens when marketing runs a campaign and traffic spikes to 10,000? Without scalability patterns, the answer is either "it crashes" or "you've been paying for 10,000-user capacity that sits idle 99% of the time." Neither is acceptable. Scalability is the ability to handle increased load without degrading performance — and equally importantly, to scale down when load decreases to avoid wasting money.

This section covers the architectural patterns that enable elastic scaling: loosely coupled architectures that prevent bottlenecks, serverless and container platforms that scale automatically, and Auto Scaling strategies that respond to the right metrics. Unlike monolithic architectures that scale vertically (bigger server), these patterns scale horizontally (more instances).