Reverse proxy concept in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Role of a Reverse Proxy in Web Architecture

Which of the following best describes the primary role of a reverse proxy in a web system?

A It directly serves static files without contacting backend servers.

B It forwards client requests to backend servers and can provide load balancing and caching.

C It acts as a client to fetch data from the internet on behalf of the server.

D It stores user credentials and manages authentication tokens.

💡 Hint

Think about what a reverse proxy does between clients and servers.

A reverse proxy sits in front of backend servers, forwarding client requests to them. It can also balance load, cache responses, and improve security.

❓ Architecture

intermediate

Reverse Proxy Placement in System Architecture

Where is a reverse proxy typically placed in a web application architecture?

A Directly inside the backend database to optimize queries.

B Between the backend servers and the database to manage data flow.

C On the client device to cache server responses locally.

D Between the client and the backend servers, acting as an intermediary.

💡 Hint

Consider the flow of requests from users to servers.

A reverse proxy is placed between clients and backend servers to intercept and manage incoming requests.

❓ scaling

advanced

Scaling Backend Servers with Reverse Proxy

How does a reverse proxy help scale backend servers in a high-traffic web application?

A By distributing incoming requests evenly across multiple backend servers to prevent overload.

B By storing all user sessions locally to reduce backend load.

C By encrypting all data between backend servers and clients to improve security.

D By replacing backend servers with a single powerful server to handle all requests.

💡 Hint

Think about how load balancing works in web systems.

A reverse proxy can distribute client requests across multiple backend servers, balancing load and improving scalability.

❓ tradeoff

advanced

Tradeoffs of Using a Reverse Proxy

Which is a common tradeoff when introducing a reverse proxy into a system?

A Directly exposes backend servers to the internet, increasing risk.

B Eliminates the need for backend servers, reducing complexity.

C Adds an extra network hop which can increase latency but improves security and scalability.

D Removes all caching capabilities from the system, reducing performance.

💡 Hint

Consider both benefits and costs of adding components in a network path.

While a reverse proxy adds an extra step in request handling, it improves security, caching, and load balancing, which outweighs the slight latency increase.

❓ estimation

expert

Estimating Reverse Proxy Capacity for Traffic Load

A reverse proxy handles 10,000 requests per second. Each request averages 500KB response size. What is the approximate outgoing bandwidth needed for the reverse proxy?

A About 50 Gbps

B About 5 Gbps

C About 500 Mbps

D About 50 Mbps

💡 Hint

Calculate bandwidth = requests per second × response size in bits.

10,000 requests/s × 500KB = 5,000,000 KB/s = 5 GB/s. Convert to bits: 5 GB/s × 8 = 40 Gbps. But 500KB is 0.5MB, so 10,000 × 0.5MB = 5,000 MB/s = 5 GB/s. Actually, 5 GB/s × 8 = 40 Gbps. The correct option closest is 5 Gbps, so re-check units: 500KB = 500 × 1024 bytes = 512,000 bytes = 4,096,000 bits. 10,000 × 4,096,000 bits = 40,960,000,000 bits/s = 40.96 Gbps. So correct is about 40 Gbps, closest option is 50 Gbps (D). So correct answer is D.

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