TodayILearned
System Design lessons
One fullstack engineering concept every day — taught deeply, then compressed into a public post.
What is caching?
And when does it bite you?
Load balancing — distributing traffic
One server can't handle it all. Here's how you spread the load — and the tradeoffs of each strategy.
Rate limiting — protecting your API
A load balancer distributes traffic. A rate limiter caps it. Here are the four algorithms and the tradeoff each one makes.
Message queues — when the request can't wait for the work
A load balancer distributes requests synchronously. A message queue decouples them asynchronously — the producer fires and forgets, the consumer processes at its own pace.
API Gateway — The Front Door
Load balancing distributes traffic. Rate limiting caps it. Caching skips work entirely. An API gateway does all three — plus authentication, routing, and protocol translation — at a single entry point. It's the composition layer where every previous lesson converges.