Reverse proxy concept in HLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a reverse proxy?

A reverse proxy is a server that sits between clients and backend servers. It receives client requests and forwards them to the appropriate backend server, then returns the server's response to the client.

intermediate

How does a reverse proxy improve security?

It hides the backend servers' details from clients, filters requests, blocks malicious traffic, and can enforce SSL/TLS encryption, protecting the backend servers from direct exposure.

beginner

Name two common uses of a reverse proxy.

1. Load balancing to distribute client requests across multiple servers. 2. Caching content to reduce backend load and improve response times.

intermediate

What is the difference between a reverse proxy and a forward proxy?

A reverse proxy serves backend servers and clients, hiding servers from clients. A forward proxy serves clients and hides clients from servers, often used to control client access to the internet.

intermediate

How does a reverse proxy help with scalability?

By distributing incoming requests to multiple backend servers, it prevents any single server from becoming overloaded, allowing the system to handle more users smoothly.

What role does a reverse proxy play in a web system?

A It acts as a client to access the internet

B It forwards client requests to backend servers

C It stores data permanently

D It replaces the backend servers

A reverse proxy receives client requests and forwards them to backend servers.

Which of the following is NOT a benefit of using a reverse proxy?

A Directly storing user data

B Load balancing requests

C Hiding backend server details

D Caching responses

Reverse proxies do not directly store user data permanently; they may cache responses temporarily.

How does a reverse proxy improve security?

A By exposing backend servers to clients

B By storing client passwords

C By hiding backend servers and filtering traffic

D By replacing firewalls

It hides backend servers and filters incoming traffic to block threats.

What is a common use case for a reverse proxy?

A Distributing requests across servers

B Replacing DNS servers

C Encrypting client devices

D Controlling client internet access

Reverse proxies commonly distribute client requests to multiple backend servers.

Which statement best describes a forward proxy compared to a reverse proxy?

A Forward proxy hides backend servers

B Forward proxy forwards requests to backend servers

C Forward proxy caches backend data

D Forward proxy hides clients from servers

A forward proxy hides clients from servers, unlike a reverse proxy.

Explain what a reverse proxy is and how it works in a simple web system.

Think of it as a middleman between your browser and the website servers.

Describe three benefits of using a reverse proxy in system design.

Consider how it helps protect servers and handle many users.

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