Layer 4 vs Layer 7 load balancing.

also: Layer 7 load balancing · Layer 4 load balancing · Layer 7 load balancer · Layer 4 load balancer · L7 load balancer · L4 load balancer · L7 load balancing · L4 load balancing

L4 balancers route by IP and port without reading the payload; L7 balancers read HTTP and route by path, headers or cookies.

the two-minute refresher

Layer 4 = transport (TCP/UDP): sees IPs and ports only, very fast, protocol agnostic.
Layer 7 = application (HTTP): can route /api to one pool and /static to another, use cookies, rewrite headers.
L7 must terminate TLS to read requests; L4 can pass encrypted traffic straight through.
Rule of thumb: L4 for raw speed and non-HTTP protocols, L7 for smart HTTP routing.

Where the course teaches it

W00 · Part 2Infrastructure Building Blockslearn it →W00 · Part 6System Design Terminology & Theoryrevisit →

Related concepts

Load balancer
OSI model
TLS