Proxy Protocol

ELI5 — The Vibe Check

Proxy Protocol passes the real client IP through load balancers and proxies without modifying the HTTP headers. When your traffic goes through 3 proxies, the backend still knows the original client's IP address. It's a TCP-level envelope that says 'by the way, the actual sender is...'

Real Talk

Proxy Protocol is a network protocol (v1: human-readable, v2: binary) that conveys original client connection information (IP, port, protocol) across proxy and load balancer layers. Unlike X-Forwarded-For headers, it works at the transport layer and supports non-HTTP protocols. Supported by HAProxy, AWS NLB, and Nginx.

When You'll Hear This

"Proxy Protocol preserves the client IP through our NLB so our app sees real addresses." / "We enabled Proxy Protocol v2 on the NLB — the binary format is more efficient than v1."