Why Reverse proxy concept in HLD? - Purpose & Use Cases

The Big Idea

Discover how a simple 'middleman' can save your system from chaos and crashes!

The Scenario

Imagine you run a busy restaurant where customers come in all at once, but you only have one small door to let them in. You try to manage the crowd yourself, answering questions, directing people, and handling orders all at once.

The Problem

This manual way is slow and confusing. Customers get frustrated waiting in line. You might miss some orders or send people to the wrong tables. It's hard to keep track of everything and fix problems quickly.

The Solution

A reverse proxy acts like a smart receptionist at the door. It welcomes customers, directs them to the right tables, handles simple questions, and balances the crowd so no one area gets overwhelmed. This makes the whole restaurant run smoothly and customers stay happy.

Before vs After

✗ Before

client -> server1
client -> server2
client -> server3

✓ After

client -> reverse proxy -> server1
                     -> server2
                     -> server3

What It Enables

It enables smooth traffic flow, better security, and easy scaling by managing requests before they reach your servers.

Real Life Example

Big websites like online stores use reverse proxies to handle millions of visitors, directing each to the right server without slowing down or crashing.

Key Takeaways

Manual request handling causes delays and errors.

Reverse proxy smartly routes and balances traffic.

This improves performance, security, and reliability.

Practice

1. What is the primary role of a reverse proxy in a web system?

easy

A. It stores data permanently like a database.

B. It receives client requests and forwards them to backend servers.

C. It acts as a client to send requests to other servers.

D. It directly serves static files without contacting servers.

Solution

1. Step 1: Understand the role of reverse proxy

   A reverse proxy acts as an intermediary between clients and backend servers, receiving requests from clients.

2. Step 2: Identify what it does with requests

   It forwards these requests to the appropriate backend servers for processing, then returns the response to the client.

3. Final Answer:

   It receives client requests and forwards them to backend servers. -> Option B

4. Quick Check:

   Reverse proxy role = Forward requests [OK]

Hint: Reverse proxy forwards client requests to servers [OK]

Common Mistakes:

• Confusing reverse proxy with database
• Thinking reverse proxy acts as a client
• Assuming it serves files directly without servers

2. Which of the following is a correct function of a reverse proxy?

easy

A. Load balancing incoming client requests across servers.

B. Storing user session data permanently.

C. Generating dynamic web pages on the server.

D. Directly connecting clients to databases.

Solution

1. Step 1: Identify reverse proxy functions

   Reverse proxies distribute incoming client requests to multiple backend servers to balance load and improve performance.

2. Step 2: Eliminate incorrect options

   Storing session data, generating pages, or direct DB connections are not reverse proxy tasks.

3. Final Answer:

   Load balancing incoming client requests across servers. -> Option A

4. Quick Check:

   Reverse proxy function = Load balancing [OK]

Hint: Reverse proxy balances load, not stores data [OK]

Common Mistakes:

• Confusing reverse proxy with application server
• Thinking it stores session data
• Assuming it generates web pages

3. Consider a system where a reverse proxy receives 1000 requests per second and forwards them evenly to 4 backend servers. How many requests per second does each backend server receive?

medium

A. 4 requests per second

B. 4000 requests per second

C. 250 requests per second

D. 1000 requests per second

Solution

1. Step 1: Understand load distribution

   The reverse proxy evenly splits 1000 requests among 4 servers, so each gets an equal share.

2. Step 2: Calculate requests per server

   1000 requests ÷ 4 servers = 250 requests per server per second.

3. Final Answer:

   250 requests per second -> Option C

4. Quick Check:

   1000 ÷ 4 = 250 [OK]

Hint: Divide total requests by number of servers [OK]

Common Mistakes:

• Multiplying instead of dividing
• Confusing total with per server requests
• Ignoring even distribution

4. A reverse proxy is configured to cache responses but clients report stale data. What is the most likely cause?

medium

A. The cache expiration time is set too long.

B. The reverse proxy is not forwarding requests.

C. Backend servers are down.

D. Clients are bypassing the reverse proxy.

Solution

1. Step 1: Analyze caching behavior

   If clients get stale data, it means cached responses are not refreshed frequently enough.

2. Step 2: Identify cause of stale cache

   Setting cache expiration too long causes the reverse proxy to serve old data instead of fresh responses.

3. Final Answer:

   The cache expiration time is set too long. -> Option A

4. Quick Check:

   Long cache time = stale data [OK]

Hint: Check cache expiration for stale data issues [OK]

Common Mistakes:

• Assuming backend servers are down without checking
• Thinking reverse proxy stops forwarding requests
• Ignoring cache settings

5. You want to design a scalable web system using a reverse proxy that handles SSL termination, load balancing, and caching. Which of the following is the best architectural choice?

hard

A. Place the reverse proxy behind backend servers to handle load balancing.

B. Let each backend server handle SSL and caching individually without a reverse proxy.

C. Use a reverse proxy only for caching, and let clients connect directly to backend servers for SSL.

D. Use a reverse proxy in front of multiple backend servers, configure SSL termination and caching on it.

Solution

1. Step 1: Understand reverse proxy capabilities

   A reverse proxy can handle SSL termination, load balancing, and caching centrally, simplifying backend servers.

2. Step 2: Evaluate architectural options

   Placing the reverse proxy in front of backend servers allows it to manage SSL and cache efficiently, improving scalability and security.

3. Final Answer:

   Use a reverse proxy in front of multiple backend servers, configure SSL termination and caching on it. -> Option D

4. Quick Check:

   Reverse proxy front = SSL, load balance, cache [OK]

Hint: Put reverse proxy in front for SSL and load balance [OK]

Common Mistakes:

• Letting backend servers handle SSL separately
• Placing reverse proxy behind servers
• Splitting SSL and caching between clients and servers