What Is a Reverse Proxy?

What Is a Reverse Proxy?

A reverse proxy is a server that accepts inbound requests from the internet (clients) and routes them to one or more backend servers on behalf of those servers. The key defining characteristic: the client thinks it is communicating with the destination server, but is actually communicating with the proxy. The actual backend servers are opaque to the client — the reverse proxy is the public face of the server infrastructure.

The "reverse" in reverse proxy refers to the opposite direction of service compared to a forward proxy. A forward proxy is configured by and serves clients — it helps clients reach servers. A reverse proxy is configured by and serves servers — it helps servers handle clients. Both are intermediaries, but they serve opposite parties in the communication.

Common reverse proxy implementations include:

• nginx — The most widely deployed web server/reverse proxy. Used by ~34% of all websites worldwide (Netcraft, 2026)
• HAProxy — High-performance TCP/HTTP load balancer. Used by GitHub, Instagram, Airbnb
• Caddy — Modern reverse proxy with automatic TLS certificate management
• Cloudflare — Cloud-based reverse proxy and CDN protecting millions of websites
• AWS ALB (Application Load Balancer) — Managed reverse proxy on AWS infrastructure
• Traefik — Container-native reverse proxy for Kubernetes/Docker environments

Core Functions of a Reverse Proxy

Reverse proxies perform multiple critical functions simultaneously, which is why they are ubiquitous in modern web infrastructure:

Load Balancing: Distributing incoming requests across multiple backend servers is the most prominent function. When traffic volume exceeds what a single server can handle, horizontal scaling with a load-balanced reverse proxy allows near-linear throughput scaling. Common algorithms include round-robin (cycling through servers equally), least-connections (sending to the server with the fewest active connections), IP hash (always routing the same client IP to the same backend for session affinity), and weighted distribution (giving higher-capacity servers proportionally more traffic).

TLS Termination: Instead of configuring TLS on every backend server individually, the reverse proxy handles TLS termination — accepting encrypted HTTPS connections from clients, decrypting them, and forwarding plaintext HTTP to the backend servers over the internal network. This centralizes TLS certificate management, simplifies backend server configuration, and allows the internal network to use fast unencrypted connections between the proxy and backends (assuming the internal network is trusted).

Content Caching: Reverse proxies can cache responses from backend servers and serve subsequent identical requests from cache without hitting the backends. This is particularly effective for static assets (images, CSS, JS), API responses with stable data, and frequently-accessed pages. Varnish Cache is purpose-built for this function and handles millions of requests per second. nginx's proxy_cache module and Cloudflare's CDN caching layer perform the same function.

DDoS Protection: Reverse proxies are ideally positioned to absorb and mitigate DDoS attacks before they reach backend servers. Cloudflare's global Anycast network, for example, distributes attack traffic across 300+ edge nodes worldwide, absorbing volumetric DDoS attacks (up to 71+ Tbps) without the backend servers ever receiving the malicious traffic. Rate limiting, IP blocking, CAPTCHAs, and bot management are all implemented at the reverse proxy layer.

SSL Certificate Management: Modern reverse proxies like Caddy and Traefik handle automatic TLS certificate provisioning via Let's Encrypt ACME protocol, eliminating manual certificate management overhead. Certificates are automatically renewed before expiration.

Request Routing: Reverse proxies route requests to different backend servers based on request attributes: URL path (/api/* to API servers, /static/* to object storage), hostname (multiple virtual hosts on a single IP), HTTP method, geographic origin, or custom headers. This enables microservices architectures where different services handle different URL paths.

Reverse Proxy vs CDN: What's the Difference?

A Content Delivery Network (CDN) is, at its core, a globally distributed reverse proxy network. The distinction is scale and geography: a traditional reverse proxy runs in one or a few data centers, while a CDN operates hundreds of Points of Presence (PoPs) around the world, serving cached content from the edge node nearest to each client.

Cloudflare, Akamai, Fastly, and AWS CloudFront are all CDNs that function as globally distributed reverse proxies. When a website owner enables Cloudflare, they update their DNS to point to Cloudflare's anycast IPs. All client requests go to the nearest Cloudflare PoP (the reverse proxy layer), which serves cache hits locally and forwards cache misses to the origin server. This provides latency reduction, bandwidth offloading, DDoS protection, and automatic TLS — all functions of a reverse proxy, at global scale. The website is a transparent reverse proxy scenario from the client's perspective — they connect to cloudflare.example.com without any awareness that their traffic is being intermediated.

Security Benefits of Reverse Proxies

Reverse proxies provide substantial security benefits by placing a hardened, feature-rich intermediary between the internet and backend servers:

Backend Server Obscurity: Backend servers' real IP addresses, operating systems, and application framework versions are hidden from clients. Attackers scanning for vulnerable software versions cannot target backend servers directly — they can only interact with the reverse proxy's hardened public interface.

Web Application Firewall (WAF): Reverse proxies like ModSecurity (nginx module), Cloudflare WAF, and AWS WAF inspect incoming requests for attack patterns — SQL injection, XSS, CSRF, path traversal, and OWASP Top 10 vulnerabilities. Malicious requests are blocked before reaching backend application code.

Rate Limiting: Reverse proxies implement per-IP, per-user, or per-endpoint rate limiting to prevent abuse, brute-force attacks, and scraping. nginx's limit_req module and Cloudflare's rate limiting feature provide this at the proxy layer without requiring application code changes.

Mutual TLS (mTLS): For API security, reverse proxies can enforce mutual TLS authentication — requiring clients to present a valid certificate in addition to the standard server certificate. This is used in zero-trust network architectures and service-to-service authentication in microservices.

Reverse Proxy vs Forward Proxy: Decision Guide

Choosing between a reverse proxy and a forward proxy depends on whose interests you're serving and the direction of traffic flow:

Use a forward proxy when: You control the clients and want to anonymize, filter, or cache their outbound internet traffic. Web scraping infrastructure, corporate internet filtering, and privacy tools all require forward proxies. All commercial proxy providers (see our provider comparison) operate forward proxy networks.

Use a reverse proxy when: You control the servers and want to manage inbound client traffic. Scaling a web application across multiple servers, adding TLS, protecting against DDoS, implementing caching, or routing API traffic to different microservices all require reverse proxies. Every production web application should have a reverse proxy layer.

Frequently Asked Questions About Reverse Proxies

Internal Resources on Reverse Proxy and Web Infrastructure