Day 1: the big picture. Day 2: databases. Day 3: caching, and how it's really a consistency problem in disguise. Today: load balancing — how traffic actually gets spread across servers, and the ways that can quietly go wrong.
Why Load Balancers Exist
Once you've horizontally scaled (Day 1 flashback) and have multiple servers instead of one, something needs to decide which server handles which request. That's the load balancer's job: sit between the client and your fleet of servers, and distribute incoming traffic so no single server gets overwhelmed while others sit idle.
It sounds simple — "just spread the requests out" — but how you spread them out turns out to matter a lot.
Load Balancing Algorithms
