Overview
Layer-4 balancing forwards packets/connections based on IP and port without looking inside — extremely fast and protocol-agnostic, but it cannot make content-aware decisions. Layer-7 balancing terminates the connection, reads the HTTP request, and can route by URL path, hostname, headers or cookies, do TLS termination, retries, and sticky sessions — at a higher per-request cost.
L4 load balancing vs L7 load balancing: key differences
| L4 load balancing | L7 load balancing | |
|---|---|---|
| Operates at | HTTP (application) layer | TCP/UDP (transport) layer |
| Routes by | Path, host, header, cookie | IP, port |
| Speed | Slightly higher overhead | Very fast |
| Features | TLS, retries, rewrites, sticky | Minimal, protocol-agnostic |
| Examples | Nginx, Envoy, ALB | LVS, NLB, HAProxy (L4 mode) |
When to use L4 load balancing
You need content-aware routing — path/host-based microservice routing, TLS termination, A/B, sticky sessions, web traffic in general.
When to use L7 load balancing
You need raw speed and protocol-agnostic forwarding (non-HTTP traffic, extreme throughput) and do not need to inspect requests.
Verdict
Use L7 for HTTP services where smart routing and TLS matter (the common case); use L4 when you need maximum throughput or are balancing non-HTTP traffic. Large stacks layer L4 in front of L7.
Common questions
What is the difference between L4 and L7 load balancing?
L4 routes by IP/port without inspecting content (fast, protocol-agnostic); L7 understands HTTP and routes by path/host/headers, enabling TLS termination, retries and sticky sessions.
Is L7 slower than L4?
Per request, slightly — it terminates the connection and parses HTTP. For most web traffic the overhead is negligible and worth the routing flexibility.