How Load Balancers Actually Pick a Server | Round Robin, Least Connections, IP Hash

Five servers. A million requests a second. Which server gets the next request? The wrong answer brings down your fleet. The right answer is one of six algorithms, and pros pick a different one for every job. Today you learn all six, side by side.

This video walks the load balancing chapter the way it actually works in production. We start with the load balancer's role: a host at the door routing every request to a backend server. We cover health checks, the first job of every load balancer, the thing that decides whether a server is even eligible to receive traffic. Then we walk every standard algorithm that runs in NGINX, HAProxy, AWS Application Load Balancer, and Cloudflare. Round robin. Least connections. Least response time. Least bandwidth. Weighted round robin. I P hash for sticky sessions.

The core demo is a side by side comparison. Three pools, four backends each, one weak backend in each pool. Same request stream hitting all three. Watch the live imbalance counter and see why round robin falls behind when one node is slow, why least connections keeps the pool balanced, and why weighted round robin handles the uneven case cleanly.

In this lesson you will see:
- The role of a load balancer between client and backend servers
- Why health checks come first and how a sick server gets pulled from the pool
- All six standard algorithms with one line of intuition each
- A live three way comparison: round robin vs least connections vs weighted on the same stream
- Why the imbalance number for weighted round robin behaves differently when one server is weaker
- I P hash and sticky sessions: how to keep a user pinned to one backend for shopping carts and login state
- Why the load balancer is itself a single point of failure and how active passive clustering fixes it
- Where this actually runs: NGINX, HAProxy, AWS A L B, Cloudflare
- A six point recap you can keep in your head for the next system design interview

If you have ever wondered why your service stays up while servers come and go, or why one wrong algorithm choice can cascade-fail an entire fleet, this is the lesson.

If this is your first system design tutorial, start with our previous video on consistent hashing or our intro to vertical and horizontal scaling. Subscribe for more system design explained from first principles.

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Видео How Load Balancers Actually Pick a Server | Round Robin, Least Connections, IP Hash канала Finance In Motion