Adapted from Mastering System Design from Basics to Cracking Interviews (Udemy) — https://www.udemy.com/course/mastering-system-design-from-basics-to-cracking-interviews/
Why are proxies used?
- Security: Hiding internal network structures or filtering malicious traffic.
- Anonymity: Masking the client's IP address.
- Caching: Storing copies of frequently accessed resources to reduce latency and bandwidth.
- Traffic Control: Restricting access to certain websites or managing bandwidth.
What is a Forward Proxy?
A Forward Proxy (often just called a "proxy") sits between a client (or a private network) and the internet. It is used by clients to access resources on the wide web.
Common Use Cases:
- Privacy & Anonymity: The destination server sees the proxy's IP address instead of the user's.
- Content Filtering: Organizations use them to restrict access to certain websites or categories.
- Bypassing Geo-restrictions: Accessing content that is blocked in a specific region.
- Caching: Speeding up browsing by serving local copies of web pages.
What is a Reverse Proxy?
A Reverse Proxy sits between the internet and identity/backend servers. It is used by servers to handle requests from clients, providing an additional layer of abstraction and control.
Common Use Cases:
- Load Balancing: Distributing incoming traffic across multiple backend servers to prevent overload.
- Security & DDoS Protection: Hiding the identity and structure of backend servers to protect them from direct attacks.
- SSL Termination: Offloading the process of decrypting SSL/TLS traffic to the proxy, reducing the load on backend application servers.
- Caching & Compression: Reducing the load on backend servers by caching static content and compressing data before sending it to the client.
Interview Questions & Answers
Deepen your understanding of Proxy servers with these common technical interview questions and structured answers.
1. What is a proxy server, and why is it used?
A proxy server is an intermediary system that sits between a client and a destination server. It forwards requests, receives responses, and relays them back to the client.
Why is a Proxy Server Used?
- Security & Privacy – It hides the client’s or server’s identity by masking IP addresses. - Caching & Performance Optimization – Frequently requested content is served faster. - Traffic Control & Load Balancing – Helps distribute traffic evenly across multiple servers. - Content Filtering – Blocks access to restricted or harmful content.
2. Explain the key differences between a forward proxy and a reverse proxy.
Forward Proxy
- Position: Sits between clients and the internet.
- User Goal: Used by clients to access external resources securely or anonymously.
- Example Tools: Squid Proxy, VPNs, Tor.
Reverse Proxy
- Position: Sits between users and backend servers.
- Server Goal: Used by servers to manage, secure, and optimize incoming traffic.
- Example Tools: Nginx, HAProxy, Cloudflare.
Comparison Table
| Feature | Forward Proxy | Reverse Proxy |
|---|---|---|
| Position | Between client and internet | Between user and backend servers |
| Purpose | Client anonymity, access control | Server protection, load balancing |
| Common Users | End-users, enterprises | Hosting providers, data centers |
3. How does SSL termination work in a reverse proxy?
SSL termination is the process where the reverse proxy decrypts HTTPS traffic before forwarding it to backend servers.
Benefits:
- ✅ Reduces Server Load – Backend servers don’t handle decryption.
- ✅ Improves Performance – Faster response times.
- ✅ Centralized Security – Easier to manage SSL certificates.
Final Thoughts
Understanding Forward Proxy vs. Reverse Proxy is essential for system design. If you want privacy, use a Forward Proxy. If you want server protection & load balancing, use a Reverse Proxy.