In technical terms, a reverse proxy is a server that retrieves resources on behalf of a client from one or more servers. These resources are returned to the client as though they originated from the reverse proxy server itself.
Unlike a forward proxy, which is an intermediary for clients who want to request resources from other servers, a reverse proxy appears to the client like an ordinary web server. Behind the scenes, however, the reverse proxy is interfacing with one or more servers, handling the complex details of negotiation between servers to satisfy the client’s request.
Under the Hood: How Reverse Proxies Work
At the heart of a reverse proxy’s operation is the HTTP request/response cycle. When a client device sends an HTTP request, the reverse proxy accepts this request. It then makes its own request to the appropriate backend server(s) on behalf of the client.
Once the backend server processes the request and sends a response, the reverse proxy receives this response. It can then manipulate the response (if necessary), before forwarding it back to the client.
From the client’s perspective, it appears as though they’re communicating directly with the reverse proxy, not the backend servers. From the backend servers’ perspective, they’re only interacting with the reverse proxy.
Benefits of Reverse Proxies
Decoupling Clients from Services
In distributed systems, such as in the case of a micro-services architecture, where an application is composed of many small, independently deployable services, a reverse proxy can be used as an API gateway. This gateway routes incoming requests to the appropriate services, which aids in decoupling the client from the services, and facilitates service discovery and versioning.
In a load balancing configuration, the reverse proxy distributes incoming requests to multiple backend servers. This distribution is based on various algorithms, such as round robin, IP hash, or least connections, to name a few.
The goal is to prevent any single server from becoming a bottleneck, thereby improving overall service performance and reliability. This is particularly crucial for high-traffic websites and applications.
Security and Anonymity
Reverse proxies provide an additional layer of defense by shielding backend servers from direct client access. They can perform tasks like SSL termination, where the reverse proxy handles incoming SSL connections, decrypts the requests, and manages the complex process of encrypting and decrypting communication between the client and the server.
Caching and Compression
A reverse proxy can also cache content from backend servers. If the cache has a stored response that fulfills a client’s request, the reverse proxy can deliver that response directly to the client, bypassing the backend server and speeding up response times.
Similarly, reverse proxies can perform gzip compression on outgoing data from the server, reducing the size of data transmitted and improving load times for clients with slower internet connections.
A great example of this can be seen in Content Delivery Networks (CDN) where reverse proxies are deployed at edge locations around the world to cache and serve content closer to users, improving response times and reducing bandwidth usage.
Examples of Reverse Proxies
Nginx, when used as a reverse proxy, can handle and proxy HTTP, WebSocket, and even gRPC requests. It supports dynamic configuration and load balancing algorithms like least connections and IP hash, making it highly customizable for different use cases.
Apache HTTP Server with mod_proxy
Apache HTTP Server, with the help of mod_proxy module, can operate as a reverse proxy. It supports a variety of protocols (not just HTTP), and can perform functions like URL rewriting and sticky sessions, wherein client requests are sent to the same backend server for the duration of a session.
HAProxy is specifically designed for high availability environments and large volumes of traffic. It offers advanced load-balancing algorithms and robust health checks, ensuring that requests are only routed to servers that are known to be operational.
AWS Elastic Load Balancing (ELB)
AWS ELB offers three types of load balancers that all operate as reverse proxies: the Classic Load Balancer, the Application Load Balancer (HTTP/HTTPS traffic), and the Network Load Balancer (TCP, UDP, and TLS traffic). ELB can handle the varying load of your application traffic in a single Availability Zone or across multiple Availability