How Load Balancers Work
One address, many servers — and the user never notices.
A single server has a ceiling. A load balancer sits in front of a pool of servers, spreading incoming requests so no one machine is overwhelmed and any can fail without taking the site down.
A
🌍
Clientsmany requests
B
⚖️
Load balancerone entry point
C
🖥️
Server poolN backends
D
✅
Responsefast & even
Legend — how to read this diagram
A–DComponentsthe parts involved, labelled in the diagram
●Requestdata travelling outward
●Responsedata returning
1 2 3Walkthroughnumbered steps below run in order
How it decides where to send you
- Round robin. Rotate through servers in order — simple and even when requests are similar.
- Least connections. Send to whichever server is handling the fewest active requests.
- Hashing. Route by a key (like client IP) so a user keeps hitting the same backend.
- Health checks. Continuously probe servers; pull unhealthy ones out automatically.
Layer 4 vs Layer 7
L4. Balances by IP and port — fast, protocol-agnostic, no visibility into the request.
L7. Reads HTTP, so it can route by path or header, terminate TLS, and cache.
Sticky sessions. Pin a user to one server when state lives there, at the cost of even spread.
One-line mental model:
Put one smart doorway in front of many workers, and you get scale and fault tolerance for free.
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