Originally published at spectredev.xyz. Cross-posted here for the Dev.to community.
Building APIs that hold up under real traffic takes more than fast code. Here's how rate limiting, versioning, and idempotency work and when they matter most.
An API that works fine at 100 requests per second can become a liability at 10,000. Not because the logic changed, but because the assumptions baked into the design stop holding at scale. Clients retry aggressively. Traffic spikes unpredictably. Downstream services slow down and back-pressure propagates upstream. Payment confirmations arrive twice.
Most of these failure modes are predictable. The patterns that prevent them rate limiting, versioning, and idempotency aren't exotic engineering. They're table stakes for any API that handles real traffic. The problem is most teams implement them as afterthoughts, bolted on when something has already broken in production.
This post is about building them in from the start.
