Proxies in System Design

In modern system design, proxy servers play a crucial role in improving performance, enhancing security, and ensuring scalability. A proxy acts as an intermediary between a client and the destination server, enabling features like load balancing, caching, anonymity, and more.

Types of Proxies

1. Forward Proxy

 

Position: Between the client and the internet.
Function: Handles requests from clients and forwards them to the appropriate server.

Use Cases:

• Hiding client IP addresses for privacy
• Caching frequently accessed content
• Filtering requests (e.g., blocking restricted websites)

How to use:

• Configure client to use proxy for outbound traffic.
• Use squid (recommended) - traditionally used as a forward proxy (and sometimes transparent proxy). It was built for caching web content and controlling outbound traffic.
• Script:

# squid.conf

http_port 3128

acl allowed_clients src 192.168.1.0/24

http_access allow allowed_clients

# Optional: block certain domains

acl blocked_sites dstdomain .facebook.com .youtube.com

http_access deny blocked_sites

• Clients configure their browser to use http://proxy-server:3128.
• NOTE: These are not production scripts, please modify accordingly.

2. Reverse Proxy

Position: Between the internet and backend servers.
Function: Accepts requests on behalf of servers and distributes them efficiently.

Use Cases:

• Load balancing across multiple servers
• Caching responses to reduce server load
• Security features like SSL termination and hiding server IPs

How to use:

• Place proxy in front of backend servers for inbound traffic.
• Use Nginx (recommended). It’s lightweight, high‑performance, and widely adopted for load balancing, SSL termination, and protecting backend servers.
• Script: 

# nginx.conf

server {

    listen 80;

    location / {

        proxy_pass http://backend_servers;

        proxy_set_header Host $host;

        proxy_set_header X-Real-IP $remote_addr;

    }

}

upstream backend_servers {

    server backend1.example.com;

    server backend2.example.com;

}

• Requests hit Nginx first, then get distributed to backend servers. 

3. Transparent Proxy

Position: Intercepts requests without altering them.
Function: Operates invisibly to the client, requiring no configuration.

Use Cases:

• Caching content for faster access
• Monitoring user activities for compliance or analytics

How to use:

• Network-level interception, no client config needed.
• Use Squid + iptables (silent interception)

# Redirect all HTTP traffic to proxy

iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 \

  -j REDIRECT --to-port 3128

# squid.conf

http_port 3128 transparent

• Clients don’t know a proxy is in place; traffic is silently intercepted. \

Benefits of Using Proxies

1. Load Balancing

Distributes incoming requests across multiple backend servers, ensuring no single server is overwhelmed. This improves scalability and reliability.

2. Caching

Stores frequently accessed content closer to the client, reducing backend load and speeding up response times.

3. Security

Adds an extra layer of protection by hiding backend server IPs and preventing direct access.

Example: Filtering out malicious traffic before it reaches the servers.

4. Anonymity

Masks the client’s IP address, providing privacy and anonymity for users browsing the internet.

Conclusion

Proxies are more than just intermediaries - they are powerful tools in system design that enhance performance, security, and user experience. Whether you’re building scalable web applications or securing enterprise systems, understanding proxies is essential for modern architecture.

NOTE: If your application is mostly about web traffic management, scaling, and securing backend APIs, Nginx(reverse-proxy) is the go‑to. If you need client-side anonymity or content filtering, Squid (forward-proxy) is the specialist.