Architecture & System Design › System Design Fundamentals · also in HTTP

Reverse Proxy

A server in front of your app that handles TLS, routing and caching.

Backend Engineer · Mid-level Frontend Engineer · Mid-level

Also known as: reverse proxy, inbound proxy, edge proxy

A reverse proxy stands in front of origin servers, facing clients on their behalf: terminating TLS, routing by host/path, caching, compressing, rate-limiting and shielding origins from direct exposure. Clients talk to the proxy as if it were the server; the proxy fulfils from cache or fetches upstream.

clients → reverse proxy (TLS, cache, route, limit) → app servers (hidden)

It’s the edge workhorse — nginx, envoy, CDNs and ingress controllers all play the role — absorbing cross-cutting HTTP concerns so applications handle business logic. Load balancing, WAF filtering and TLS termination typically ride along.

The classic mistakes:

Logic creep. Business rules in proxy config (rewrites encoding product decisions) become untested, unreviewed code in an awkward language. Proxy handles transport; apps handle meaning.
Trusting upstream blindly. “Internal” upstreams still need timeouts, health checks and validation — a hung origin holds proxy workers hostage.
Header spoofing. Backends must accept X-Forwarded-* only from the proxy; clients forging them spoof IPs and schemes. Strip at the edge, set authoritatively.
Cache poisoning via misconfiguration. Caching keyed wrong (ignoring auth headers, varying wrong) serves one user’s bytes to another. Key caches precisely; default private content to no-store.
Single proxy, no redundancy. The front door is a single point of failure unless redundant and health-checked. Run pairs; fail over automatically.
Buffering surprises. Request/response buffering changes streaming behaviour and memory profiles; tune for SSE/WebSocket/uploads explicitly rather than inheriting defaults.

How to deploy it: terminate and route at the edge, cache deliberately, distrust upstreams operationally, and keep product logic out of config. The reverse proxy is infrastructure doing HTTP’s chores — excellent at them, wrong for anything else.