What is a reverse proxy and how does it differ from a load balancer?
Reverse proxies and load balancers are both traffic management tools used in system design, but they have different roles. A reverse proxy sits in front of web servers to help with performance and security (for example, caching content and hiding servers from attackers). A load balancer distributes incoming requests across multiple servers to prevent any single server from getting overwhelmed. In this article, we'll explain each concept in simple terms, go over their key differences, and see when to use one or the other (common topics in system design technical interviews).
What is a Reverse Proxy?
A reverse proxy is a server (or service) that sits in front of backend servers (like web servers or APIs) and forwards client requests to those servers. From the client's perspective, the reverse proxy is the web server – the client never directly interacts with the actual origin servers. This setup adds a layer of abstraction and security between users and your backend systems.
Key benefits of reverse proxies:
- Security & SSL: It hides your backend servers’ IPs from the public and can block malicious traffic. A reverse proxy can also handle SSL/TLS encryption for the servers, adding a security layer and reducing their work.
- Caching & Speed: It caches popular content (pages, images) and serves it directly to users. This lightens the load on backend servers and speeds up response times.
(To learn more about forward proxies vs. reverse proxies, see our Q&A on the difference between a proxy and a reverse proxy.)
What is a Load Balancer?
A load balancer is a system (either a dedicated device or software service) that distributes incoming network requests across multiple servers. If one server can’t handle all your traffic alone, you put a load balancer in front of two or more servers running the same application. The load balancer will send each new request to one of the servers in the group (often called a server pool or cluster).
This ensures no single server is overloaded, keeping the service fast and reliable.
Reverse Proxy vs. Load Balancer: Key Differences
At first glance, reverse proxies and load balancers can appear similar – both sit between clients and servers and forward requests. In reality, their goals and use cases differ:
- Purpose & Scale: A reverse proxy mainly protects and optimizes servers (caching, security) and can even be useful with just one backend server. A load balancer’s role is to distribute traffic for scalability and high availability, and it only makes sense when you have multiple servers.
- Protocol Level: Reverse proxies generally operate at the application layer (HTTP/HTTPS), handling web requests. Load balancers can work at various layers (TCP or HTTP), so they can handle more than just web traffic (for example, balancing email or database requests).
- Advanced Features: Load balancers often include features like health checks, automatic failover, and session persistence to manage high traffic and server failures. Reverse proxies excel at caching, SSL termination, and content compression, but they usually don't offer the full suite of traffic management features of dedicated load balancers.
Despite these differences, both components often work together. You might use a load balancer to distribute traffic across several reverse proxy servers, combining their benefits. The key is using each tool for what it does best.
FAQs
Q1. Is a load balancer the same as a reverse proxy?
A: Not exactly. A load balancer is essentially a special kind of reverse proxy designed to distribute traffic across multiple servers. Not all reverse proxies do load balancing – some might just front a single server for caching or security.
Q2. When should I use a reverse proxy instead of a load balancer?
A: Use a reverse proxy to improve security, enable caching, or offload tasks (like SSL) when you have one (or a few) servers. It's ideal for protecting a small app or boosting performance. If your app runs on several servers or needs to handle heavy traffic, a load balancer is essential for distributing load.
Conclusion
Reverse proxies and load balancers are foundational elements in modern system architecture. A reverse proxy acts as the public face and protector of your servers, improving performance with caching and adding security. A load balancer keeps your services scalable and available by spreading work across servers. Knowing the difference is not only important for building resilient systems but also for tackling system design interview questions with confidence.
In practice, these technologies often work hand-in-hand: you might place a load balancer to scale out your application and also use a reverse proxy to cache content or enforce security rules.
For a deeper dive into system design basics, read our System Design Interview Fundamentals guide. Explore More: To practice with real scenarios, check out our courses Grokking System Design Fundamentals and Grokking the System Design Interview. These courses offer more technical interview tips, case studies, and hands-on exercises to level up your system design skills.
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