A reverse proxy is a server that sits between client devices and a web server, forwarding client requests to the web server and returning the server’s responses to the clients. In contrast to a forward proxy, which serves the client’s interests, a reverse proxy serves the interests of the web server.

Functions and Features of Reverse Proxy

Load Balancing

A reverse proxy can distribute network or application traffic across many servers. This process, known as load balancing, allows a company to manage more traffic than a single server can handle, providing redundancy and preventing server overloads.

SSL Termination

The reverse proxy can handle the SSL encryption/decryption process (the SSL “handshake”), offloading this task from the web servers and freeing up resources.

Caching

A reverse proxy can cache responses from a web server and, on subsequent requests, serve cached content directly to clients, reducing the load on the web server.

Compression

A reverse proxy can compress incoming data from the server before sending it to the client, reducing the amount of data sent and speeding up transmission times.

Security

A reverse proxy provides an additional layer of security, masking the topology and characteristics of backend servers from potential attackers. It can also provide other security benefits, such as protection against DDoS attacks.

Different Types of Proxies

Forward Proxy

A forward proxy, or simply “proxy,” is the opposite of a reverse proxy. It serves client requests, possibly modifying them, and sends them to the intended server. Forward proxies can bypass web filters or geographical restrictions, maintain privacy and anonymity, or cache frequently accessed content.

Reverse Proxy

As we’ve already explored, a reverse proxy stands between clients and web servers, and serves the interests of the web servers. They’re commonly used for load balancing, SSL termination, caching, and security.

Open Proxy

An open proxy is an openly available proxy to any internet user. They can be exploited for various purposes, such as sending spam emails or performing distributed denial-of-service (DDoS) attacks.

What is a proxy server?

A forward proxy and a reverse proxy essentially serve opposite functions, but the mechanisms of operation are somewhat similar. Let’s break this down further.

Forward Proxy Setup:

Let’s say you have the following setup:

  • Two client computers (Client A and Client B)
  • One forward proxy server
  • Two web servers on the Internet (Internet Server 1 and Internet Server 2)

Here’s how it would work:

  1. Client A wants to access a webpage that’s on Internet Server 1. The client sends the request to the forward proxy server.
  2. The forward proxy server receives the request from Client A and forwards it to Internet Server 1.
  3. Internet Server 1 processes the request and returns the response to the forward proxy server.
  4. The forward proxy server then forwards the response from Internet Server 1 back to Client A.
  5. The process repeats if Client B wants to access the same webpage.

In this setup, the forward proxy server acts as a gateway from the clients to the internet. The clients use the forward proxy to access the internet, and the servers on the internet only see the proxy, not the individual clients.

Reverse Proxy Setup:

Now let’s consider a setup with a reverse proxy:

  • Two client computers (Client A and Client B)
  • One reverse proxy server
  • Two origin servers (Server 1 and Server 2)

Here’s how it would work:

  1. Client A wants to access some content that’s on Server 1. Instead of connecting directly to Server 1, the client sends the request to the reverse proxy server.
  2. The reverse proxy server receives the request from Client A and forwards it to Server 1.
  3. Server 1 processes the request and returns the response to the reverse proxy server.
  4. The reverse proxy server then forwards the response from Server 1 to Client A.
  5. The process repeats itself if Client B wants to access the same content.

In this setup, the reverse proxy server acts as a gateway from the internet to the servers in a network. The clients on the internet use the reverse proxy to access the servers on the web, and the servers in the network only see the proxy, not the individual clients.

So, comparing the two setups, the key difference is the direction of the traffic:

  • In a forward proxy setup, the proxy handles outbound traffic from a network to the internet. Clients inside the web use it to access the internet.
  • In a reverse proxy setup, the proxy handles inbound traffic from the internet to a network. Clients use it on the internet to access servers inside the network.

Implementing a Reverse Proxy

Here are a few simplified step-by-step guides on how to set up a primary reverse proxy:

Undisclosed Advantages of Reverse Proxy

A/B Testing

Using a reverse proxy can make A/B testing more efficient. The proxy can direct client requests to different server versions of a web page, which allows the performance of the other versions to be compared directly.

Serving Stale Content

When the backend servers are temporarily unavailable, a reverse proxy server can serve stale or outdated content from its cache to maintain service availability. Although the information might be outdated, it is better than no response, providing a more favorable user experience.

Hiding Information about Backend Servers

A reverse proxy can hide the IP addresses and other details of backend servers from the clients. This can make it more difficult for malicious actors to target these servers directly.

Enhanced Security

DDoS Mitigation

In a DDoS attack, an overwhelming amount of traffic is sent to a server to cause it to crash. A reverse proxy can help protect web servers from such attacks by limiting the rate of requests that each client can make.

Filtering Requests

Reverse proxies can be configured to reject requests from specific IP addresses or with certain characteristics. This can help protect the web servers from attacks that aim to exploit specific vulnerabilities.

Conclusion

In addition to their well-known benefits, reverse proxies can be used for a wide range of less-explored tasks, from SSL/TLS offloading to serving stale content when backend servers are unavailable. Furthermore, they can enhance security in several ways, such as mitigating DDoS attacks and filtering out potentially harmful requests. Therefore, employing a reverse proxy can provide significant advantages, making it a worthwhile consideration for any organization with a web presence.