Reverse Proxy

In computer networks, a reverse proxy is an application that sits in front of back-end applications and forwards client (e.g. browser) requests to those applications. Reverse proxies help increase scalability, performance, resilience and security. The resources returned to the client appear as if they originated from the web server itself.

Example scenario: A client on the Internet (cloud on the left) makes a request to a reverse proxy server (red oval in the middle). The proxy inspects the request, determines that it is valid and that it does not have the requested resource in its own cache. It then forwards the request to some internal web server (oval on the right). The internal server delivers the requested resource back to the proxy, which in turn delivers it to the client. The client on the Internet is unaware of the internal network, and cannot tell whether it is communicating with a proxy or directly with a web server.

Large websites and content delivery networks use reverse proxies, together with other techniques, to balance the load between internal servers. Reverse proxies can keep a cache of static content, which further reduces the load on these internal servers and the internal network. It is also common for reverse proxies to add features such as compression or TLS encryption to the communication channel between the client and the reverse proxy.

Reverse proxies are typically owned or managed by the web service, and they are accessed by clients from the public Internet. In contrast, a forward proxy is typically managed by a client (or their company) who is restricted to a private, internal network, except that the client can ask the forward proxy to retrieve resources from the public Internet on behalf of the client.

Reverse proxy servers are implemented in popular open-source web servers such as Apache, Nginx, and Caddy. This software can inspect HTTP headers, which, for example, allows it to present a single IP address to the Internet while relaying requests to different internal servers based on the URL of the HTTP request. Dedicated reverse proxy servers such as the open source software HAProxy and Squid are used by some of the biggest websites on the Internet.