What is a Proxy?
A proxy is an intermediary server that acts as a gateway between a client and another server (usually on the internet). It receives requests from clients and forwards them to the destination, often performing additional tasks such as security filtering, caching, or load balancing.
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.