A reverse proxy primarily serves as a load balancer for web applications.

You have a web application with multiple application servers behind a reverse proxy, and the reverse proxy takes care of distributing the oncoming traffic across these application servers. It makes your web application highly available as the reverse proxy will route traffic away from unreachable application servers during a failure. It will also become horizontally scalable as you can add more application servers as traffic grows.

But this is just one use case of the reverse proxy.

Here are 9 other things the reverse proxy can do for you:

⏳ 1. Handling Slow Clients

Application servers (like Node.js, Python/Gunicorn, or Ruby/Puma) are highly optimized for executing application logic, but they are often poor at handling slow network connections. A "slow client" (e.g., a user on a bad mobile network) who takes 30 seconds to download a response can tie up an entire application worker, preventing it from serving other users.

A reverse proxy is built for this. It will quickly receive the full response from your application server (freeing it up instantly) and then "spoon-feed" that response to the slow client at whatever pace it can handle.

🔐 2. Security and Malicious Request Filtering

A reverse proxy acts as your application's first line of defense. By never exposing your application servers directly, you gain several security advantages:

• IP Masking: Attackers can only see the IP of the reverse proxy, not your internal backend servers.
• Rate Limiting: The proxy can be configured to block or throttle IP addresses that make too many requests in a short period, mitigating basic DDoS and brute-force attacks.
• Malicious Filtering: Many reverse proxies can be configured (often as a Web Application Firewall, or WAF) to inspect requests and filter out common attacks like SQL Injection or Cross-Site Scripting (XSS) before they ever reach your code.

💨 3. Compression

Sending large files (like your site's HTML, CSS, and JavaScript) over the internet is slow. Gzip or Brotli compression can drastically reduce the size of these assets.

While your application could handle this, it's a CPU-intensive task. A reverse proxy can offload this work, compressing assets on the fly before sending them to the user. Your application serves the uncompressed file, and the proxy does the "grunt work" of compression, freeing up your app's resources.

📜 4. Simplified SSL/TLS Management

Every modern website needs HTTPS, which requires an SSL/TLS certificate. Managing these certificates—installing them, and, more important, renewing them—across multiple application servers is complex and error-prone.

A reverse proxy simplifies this with SSL termination. The proxy is the only server that speaks HTTPS to the outside world. It "terminates" the encrypted connection, then communicates with your backend servers over a fast, simple, unencrypted HTTP connection (on your private network). You only have to manage one certificate (or a wildcard) on the proxy itself.

🗺️ 5. URL Rewriting and Routing

A reverse proxy is an expert at manipulating and routing requests based on URLs. This gives you incredible flexibility:

• Have a new React app and an old legacy app? The proxy can serve your-site.com/ from the new app and your-site.com/legacy-admin from the old one.
• Running a WordPress blog for marketing? It can route your-site.com/blog to a completely separate server.
• Refactoring your app from a monolith to microservices? The proxy can route your-site.com/api/users to the "User service" and your-site.com/api/products to the "Product service."

To the end-user, it all appears to be a single, seamless application.

🖼️ 6. Serving Static Files

Application servers are for dynamic content (processing data, talking to a database). They are incredibly inefficient at serving static files like images, CSS, and JavaScript.

A reverse proxy can be configured to intercept requests for these assets (e.g., any request to /static/ or /assets/) and serve them directly from its own disk. This is lightning-fast and frees your application servers to handle only the important, dynamic requests.

📦 7. Caching

Some requests are expensive to generate but don't change often. For example, your site's homepage, a list of blog posts, or an API endpoint for product categories.

A reverse proxy can cache the responses for these requests for a set amount of time (e.g., 60 seconds). If 1,000 users request the homepage in one minute, your application server will only have to generate it once. The proxy will serve the cached copy to the other 999 users, dramatically reducing the load on your application and database.

🚀 8. Support for Advanced Features (HTTP/3, QUIC)

The web is always evolving. New protocols like HTTP/3 (which runs over QUIC) offer significant performance improvements, especially for mobile and unreliable networks.

Your application code, written in Python or Ruby, probably doesn't speak HTTP/3. But a reverse proxy (like Nginx) does. The proxy can talk to the user with the latest, fastest protocols and "translate" those requests back to plain old HTTP/1.1 for your application. You get a massive performance boost for free, with zero changes to your app code.

🛫 9. Zero-downtime deployments

When you have a reverse proxy in front of your web application, you can use it to safely migrate traffic from the old version of your app to the new version with no downtime.

Common traffic migrations strategies:

• Blue/Green Deployment: You deploy a complete, new "green" version of your application alongside the old "blue" version. The proxy continues sending all traffic to "blue." Once you've tested "green," you tell the proxy to flip 100% of the traffic over. If something is wrong, you can instantly flip it back.
• Canary Deployment: For a more gradual rollout, you can configure the proxy to send 1% of your traffic to the new version. You can monitor its performance and error rates. If all is well, you dial it up to 10%, 50%, and finally 100%.

Don't think that Blue/Green Deployment and Canary Deployment are only for microservices running on Kubernetes. You can apply the same concepts with a monolithic application using a reverse proxy.

Choosing a reverse proxy

There are many reverse proxies to choose from.

The first three that comes to my mind are Nginx (my favorite), HAproxy, and Traefik, - all open-source projects.

On the cloud, the cloud providers offer layer-7 load balancers that have certain reverse proxy features. But, these layer-7 load balancers often lack all features we mentioned here, that I am still inclined to use Nginx between the layer-7 load balancer and my web app.

In an upcoming post, I will go into details about these AWS application deployment architectures.