What is the difference between a forward proxy and a reverse proxy server?

Understanding proxies is essential for modern system architecture and technical interview preparation. In system design, proxies act as intermediaries that can improve performance, security, and scalability. Many system design interview questions probe your understanding of forward proxy vs reverse proxy servers. Grasping their differences will help you design robust networks and ace those interviews.

Technical Interview Tip: If an interviewer asks about proxies, clarify whether they mean a forward or reverse proxy, as each serves a different role in system architecture. This distinction often comes up in mock interview practice and can showcase your networking fundamentals knowledge.

What Is a Proxy Server?

In simple terms, a proxy server is an intermediary that sits between a client and a destination server, relaying requests and responses. Instead of a client communicating directly with a web server, the proxy steps in as a middleman. This extra layer can provide benefits like caching, filtering, or anonymity. There are two main types of proxies in network design: forward proxies and reverse proxies. The core difference between them comes down to who they represent and where they sit in the network.

Forward Proxy (Client-Side Proxy)

A forward proxy (often just called a "proxy") stands in front of one or more clients. It acts on behalf of clients by sending requests to other servers for them. In other words, the forward proxy is the “representative” of the client in conversations with external servers. For example, your browser might be configured to use a forward proxy server to access the web. The proxy receives your web requests and then forwards them to the target website. The site sees the proxy as the origin of the request, not your personal device.

• How it works: When a client (e.g. your computer) makes an HTTP request, it actually sends the request to the forward proxy server. The proxy then contacts the destination web server on the internet, fetches the data, and returns it to you. The external site communicates only with the proxy, never directly with your device.
• Purpose: Forward proxies are typically used to regulate and secure client traffic. They can enforce organization policies, cache responses, and mask client IP addresses for privacy. Essentially, no origin server communicates directly with the specific client; the proxy intermediates every request.
• Use cases: Common scenarios include corporate or school networks using a proxy to filter or block websites (e.g. social media) and save bandwidth via caching. Forward proxies are also used to bypass geo-restrictions or censorship by routing traffic through an allowed server. For instance, a user in a restricted network might use an HTTP forward proxy to reach a blocked site. Additionally, forward proxies provide anonymity – hiding the user’s real IP address from the destination server. A well-known example is the Tor network, which layers multiple proxy relays to anonymize web traffic.

Reverse Proxy (Server-Side Proxy)

A reverse proxy sits in front of one or more web servers and acts on behalf of those servers. It accepts incoming client requests at the network edge and then forwards them to the appropriate origin server on the backend. To the client, the reverse proxy itself appears to be the web server (the client may not even realize a proxy is involved). The reverse proxy then returns the server’s response to the client, so the client always interacts only with the proxy. In effect, the reverse proxy represents the server in the communication.

• How it works: When you visit a website that uses a reverse proxy, your request first hits the proxy server rather than the actual web server. The reverse proxy intercepts the request and checks what needs to be done. It might serve the content directly if cached, or route the request to one of the several internal servers. The client’s connection terminates at the proxy, and the proxy establishes a separate connection to the backend server to fetch data, then sends the response back to you.
• Purpose: Reverse proxies are deployed to protect and optimize server-side infrastructure. They ensure no client communicates directly with the origin servers (clients only see the proxy’s IP/hostname). This hides the identity and structure of backend servers, adding a layer of security. The reverse proxy can also offload tasks from the main servers, improving overall efficiency.
• Use cases: Typical uses of reverse proxies include load balancing (distributing incoming traffic across multiple servers) and caching static content (images, scripts, etc.) to reduce load on origin servers. Reverse proxies often handle TLS/SSL encryption (terminating HTTPS connections) so that backend servers can operate without the overhead of encryption. They can serve as a Web Application Firewall (WAF), filtering out malicious requests, and handle compression or decompression of data to speed up communications. A common example is an NGINX or Apache server configured as a reverse proxy in front of application servers. Another everyday example is a content delivery network like Cloudflare: Cloudflare’s network functions as a massive reverse proxy, caching content globally and shielding the true origin server from direct exposure.

Forward Proxy vs Reverse Proxy: Key Differences

Let’s compare forward proxies vs reverse proxies side by side. Both are proxy servers (intermediaries), but they operate in opposite directions:

• Position in Network: A forward proxy sits between the client and the internet, acting as the client’s gateway to external services. In contrast, a reverse proxy sits in front of the web server(s) on the server side, acting as an entry point for clients’ requests.
• Whom It Serves: A forward proxy serves the client’s interests – it represents one or many clients and fetches data on their behalf. A reverse proxy serves the server’s interests – it represents the server(s) and handles requests on their behalf before they reach the actual server.
• Primary Uses: Forward proxies are used for client-side tasks like content filtering, caching web responses for a group of users, and hiding clients’ identities for privacy. Reverse proxies are used for server-side tasks such as load balancing traffic, caching content to reduce server load, offloading SSL encryption, and shielding the server’s identity and internal network for security.
• Client Awareness: In many cases, using a forward proxy requires an explicit configuration on the client side (the client knows it’s using a proxy). With a reverse proxy, the process is transparent to the end user – the client thinks it’s communicating with the target server, unaware that a proxy is intermediating.
• Examples: An example of a forward proxy is a web proxy service or corporate proxy that your browser is configured to use – for instance, a company proxy that employees must go through to access external websites (enforcing company browsing policies). An example of a reverse proxy is a load balancer in front of a cluster of servers – for instance, Amazon’s Elastic Load Balancer or an NGINX instance routing incoming requests to multiple application servers. Another example is Cloudflare’s CDN, which acts as a reverse proxy, caching content and providing security features at the network’s edge.

FAQs (People Also Ask)

Q1. What is the purpose of a forward proxy? A forward proxy server is used to act on behalf of clients, typically to enhance privacy and control access. Its purposes include caching frequently requested content (to speed up client browsing), hiding the client’s IP address for anonymity, and filtering or blocking requests based on organizational policies (for example, blocking certain websites). By using a forward proxy, clients can also bypass network restrictions since the proxy can fetch data from sites that might be blocked on the client’s network.

Q2. What is the purpose of a reverse proxy? A reverse proxy server is used to stand in front of web servers to improve performance and security for those servers. Its key purposes include distributing incoming traffic across multiple servers (load balancing) to prevent overload, caching and serving static content (reducing workload on origin servers), and acting as a shield for the actual servers by hiding their identities. A reverse proxy can also enforce security rules and SSL encryption, essentially protecting backend servers from direct exposure to the internet. This makes the website more scalable and secure.

Q3. Is a load balancer the same as a reverse proxy? Yes – in fact, a load balancer is a special kind of reverse proxy. Both sit in front of backend servers, but a load balancer’s primary function is to distribute requests evenly among multiple servers. All load balancers are reverse proxies by nature (they proxy client requests to servers), but not all reverse proxies are just load balancers. A reverse proxy might perform other duties (like caching or security filtering) in addition to simple traffic distribution. In system design, you can often treat the load balancer as a reverse proxy that adds scalability.

Q4. Can one server be both a forward and reverse proxy? Typically, a server is configured as either a forward proxy or a reverse proxy, not both at the same time. The roles are distinct: a forward proxy handles outbound requests on behalf of clients, while a reverse proxy handles inbound requests on behalf of servers. In practice, software like NGINX or Squid can be configured to run in either mode, but you would set up separate proxy services for each role. It’s rare to configure a single instance to do both simultaneously, as the use cases don’t usually overlap.

Q5. Why are proxies important in system design interviews? Proxies often come up in system design interviews because they are fundamental to building scalable and secure systems. Forward proxies demonstrate concepts like caching and access control from the client side, while reverse proxies (including load balancers and CDNs) illustrate how to handle scalability, redundancy, and network security on the server side. Interviewers may ask you to design a web infrastructure where using a reverse proxy (for load balancing or caching) is key, or to explain how a forward proxy could enable certain features. Knowing the difference – and when to use each – shows that you grasp important system architecture concepts and can apply technical interview tips in practice.

Conclusion

Forward proxies vs reverse proxies boil down to whom the proxy represents: forward proxies stand in for clients, while reverse proxies stand in for servers. Forward proxies help clients by providing anonymity, caching, and access control. Reverse proxies help servers by handling load balancing, caching, encryption, and security tasks. Both types are invaluable in designing high-performance, secure systems.

In summary, understanding these proxy servers and their roles is crucial for any system architect or interviewee. They illustrate how adding an intermediary can solve scaling and security challenges in different ways. As you prepare for system design interviews, remember these key takeaways and consider how proxies fit into larger architectures.

For more foundational knowledge, check out our blog on System Design Interview Fundamentals. And if you want to dive deeper and practice these concepts, explore our Grokking the System Design Interview course. It covers system design essentials with real-world examples and mock interview practice to help you ace your next technical interview!