What Is a Reverse Proxy? Definition & Use Cases

Consider you are building a high-end financial software which processes stock transactions in real-time. The application’s servers must be secure and able to handle a huge number of requests without any slowdown.

This is where the reverse proxy comes into action. Unlike the forward proxies that control the identity of clients, a reverse proxy focuses on protecting the servers from clients and other threats from the Internet.

What Is a Reverse Proxy?

A reverse proxy is a type of server that sits in front of the one or more web servers (between the Internet and web servers) and intercepts all requests from the users before they reach the servers. Its main goal is to increase the network performance, scalability, and security.

A reverse proxy can provide robust server security by managing SSL data encryption and ensuring the backend servers are not accessible directly from the Internet. Furthermore, it can balance the incoming requests among multiple servers, preventing one server from being overloaded, ultimatly improving the server performance and minimize the downtime.

How Reverse Proxy Works?

To get a better understanding of reverse proxy, let’s discuss how reverse proxy works:

1. Client Request– A user tries accessing the web application through Device 1 or 2. The request first passes through the Internet and reaches the proxy server.
2. Request Evaluation: The reverse proxy evaluates the request and decides whether to serve the request from its cache or send it to an actual server resource.
3. Communication with Backend Servers: If not cached, the reverse proxy determines which backend server is best suited to handle the request based on the server load, content type, or specific routing rules. If cached, it returns the response through the cache.
4. Request Processing: Once the backend server processes the request, it sends the response back to the reverse proxy.
5. Caching: If caching has been enabled, the reverse proxy will cache the response generated through the resource.
6. Response Delivery: The reverse proxy sends the response back to the client.

As you can understand, this process is very much different from traditional forward proxy behaviour. Reverse proxy server mainly serves the function of protecting the backend servers from the Internet risks and users.

Forward Proxy vs Reverse proxy

A forward proxy is a type proxy server which is placed between a user’s machine and the Internet. It serves as a proxy for the user, filtering content, providing anonymity, or bypassing restrictions. For example, a school or workplace may implement a forward proxy to block access to certain websites or to monitor online activities.

This change in proxy server placement creates some significant differences between a reverse and a forward proxy:

1. Traffic Direction: Forward proxies send outgoing requests from a user to the Internet. Reverse proxies handle incoming requests from the Internet to a server.

2. Anonymity: Forward proxies provide anonymity for users, while reverse proxies protect servers by filtering incoming traffic and optimizing the load balancing.

3. Visibility: Users are aware of a forward proxy. They can configure their browser or network settings to use it. In contrast, reverse proxies are invisible to end users. They interact with it indirectly through the websites they visit.

Apart from the above differences, there is a lot shared between these 2 proxy types. The below table will give you a summary of all the similarities and differences.

Benefits of using a Reverse Proxy

Using a reverse proxy offers several key advantages, such as improved security, scalability, load balancing, and performance. 

1. Enhanced Security

• Protection from External Threats: A reverse proxy is a layer of protection that stands between users and servers and acts as a shield. It acts as a first line of defense by blocking malicious requests before they can reach in-house servers, minimize the likelihood of attacks
• SSL/TLS Termination: Generally, servers are tasked with SSL/TLS termination. However, a reverse proxy can do the encryption and decryption tasks for the backend servers, thus, freeing the resources of the servers for the critical operations. The snippet below is an Nginx setup that secures server via SSL (https) that then acts as a reverse proxy.

server {
    listen 443 ssl;
    server_name yourdomain.com;
    ssl_certificate /path/to/your_certificate.pem;
    ssl_certificate_key /path/to/your_private_key.pem;
    location / {
        proxy_pass http://your_backend_servers;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

2. Scalability

• Server Flexibility: They distribute users requests to the corresponding server, depending on the server’s current load. So, you can add or remove servers without any downtime.
• Maintenance and Upgrades: By utilizing reverse proxy, you can upgrade or do maintenance on backend servers in a sequential manner, and still maintain the whole application’s availability. For example, assume that you are in charge of a website that sells tickets and the site has to be uninterrupted 24/7. Through a reverse proxy, you can upgrade the backend servers one by one without having to take the entire service offline.

3. Load Balancing

• Traffic Distribution: A reverse proxy prevents performance bottlenecks by distributing incoming requests across multiple servers, ensuring no single server bears too much load.
• Health Checks: Modern reverse proxies can perform health checks on backend servers, redirecting traffic away from servers that are down or under heavy load. For example, in Nginx, you can set up an upstream block in your configuration file that includes health check parameters.

upstream backend_servers {
    server server1.example.com;
    server server2.example.com;
    server server3.example.com;

    zone backend 64k;

    # Health checks
    health_check interval=5 fails=2 passes=2 uri=/health;
}

server {
    listen 80;
    location / {
        proxy_pass http://backend_servers;
    }
}

4. Performance

• Content Caching: Caching frequently requested resources on the reverse proxy reduces the number of requests to the backend servers. The below example shows how to configure Nginx to cache data based on HTTP response codes.

proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=news_cache:10m max_size=1g inactive=60m use_temp_path=off;

server {
    listen 80;
    location / {
        proxy_cache news_cache;
        proxy_pass http://backend_servers;
        proxy_set_header Host $host;
        proxy_cache_valid 200 302 10m;
        proxy_cache_valid 404 1m;
    }
}

• Compression: Compression at the proxy level reduce the amount of data that needs to be sent over the network. The below Nginx configurations enable gzip compression for the following content types: HTML, CSS, JSON, JavaScript and XML.

server {
    listen 80;
    location / {
        proxy_pass http://backend_servers;
        proxy_set_header Host $host;
        gzip on;
        gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;
    }
}

Risks Associated with Using a Reverse Proxy?

Using a reverse proxy offers numerous advantages. However, like any technology, it also comes with potential risks and challenges.

1. Single Point of Failure

A reverse proxy can become a single point of failure in your network architecture if not properly managed. Since all incoming traffic to backend servers must pass through the reverse proxy, any malfunction can make the entire application inaccessible.

Solution: Consider implementing redundant reverse proxy instances and use load balancing between them to ensure availability even if one instance fails.

2. Security Vulnerabilities

While reverse proxies enhance server security, any vulnerability in the reverse proxy software can be exploited, leading to significant security breaches. 

Solution: Keep the reverse proxy software up-to-date with the latest security patches.

3. Traffic Inspection

Reverse proxies are responsible for handling sensitive data that traverses between clients and servers. If not properly secured, the sensitive data can be exposed via misconfigurations or attacks.

Solution: Ensure strong encryption for data in transmissions and rest. Conduct regular audits and reviews for configurations and access controls in order to prevent data leakage.

4. Configuration Errors

Reverse proxies require precise configuration to function correctly. Misconfigurations can lead to issues like improper routing, open vulnerabilities, or performance bottlenecks. 

Solution: Use management configuration tools and versioning systems for the tracking changes as well as facilitating the rollback in case of error.

5. Trust Relationship

Usually, reverse proxies involve strong relationships with backend servers because of user authentication and data validation. Violation of this relationship of trust can result in unauthorized access and data breaches.

Solution: Implement a strong authentication and validation framework at the global load balancer and the backend servers to protect these resources against emerging threats.

Common Uses of Reverse Proxies

Reverse proxies are a versatile tool that can be used for many purposes. Here are some common use cases of reverse proxies:

• Content Delivery Networks (CDNs) – To cache content at network edges closer to the user.
• Secure Web Gateways – To hide the identities of backend servers from potential attackers.
• High-traffic websites and applications – To distribute incoming traffic among several servers.
• Streaming Services – To perform tasks such as transcoding or adjusting the quality of video streams in real-time based on the user’s bandwidth and device capabilities.
• E-commerce platforms, Financial Services – To inspect incoming traffic for security threats.
• Mobile Web Services – To adjust content specifically for mobile devices.(optimize images and scripts)

Conclusion

A reverse proxy is a server that is placed between the internet and backend servers, improving the network performance, scalability and security. However, reverse proxies may also pose some risks, such as creating a single point of failure, security vulnerabilities due to misconfigurations, trust relationship issues, etc.

While these challenges persist, the proxies have become such an important part of modern IT infrastructures due to their load balancing, caching and SSL termination features. Hence, as developers, we must understand how different types of proxy services work to improve our application architectures. Try the best proxies for free!