Why load balancers distribute traffic in HLD - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why do load balancers distribute traffic?

Imagine a busy restaurant with many customers arriving at the same time. The restaurant manager wants to make sure no single waiter is overwhelmed. How does this relate to load balancers in system design?

Why do load balancers distribute traffic among servers?

A To increase the size of the database automatically when traffic grows.

B To store all user data centrally for faster access.

C To evenly spread incoming requests across multiple servers to prevent any one server from becoming a bottleneck.

D To encrypt all network traffic between clients and servers.

💡 Hint

Think about how sharing work helps avoid overload.

Load balancers distribute traffic to prevent any single server from getting overwhelmed, ensuring better performance and reliability.

❓ Architecture

intermediate

Which architecture best shows load balancer traffic distribution?

Given a system with multiple web servers, which architecture diagram best represents how a load balancer distributes incoming user requests?

A Users sending requests to a single web server which then forwards to a load balancer.

B Multiple web servers each receiving requests directly from users without any intermediary.

C A database server distributing queries to multiple load balancers.

D A single load balancer receiving all requests and forwarding them to multiple web servers behind it.

💡 Hint

Think about the role of the load balancer as the traffic controller.

The load balancer acts as a single entry point that distributes requests to multiple servers, balancing the load.

❓ scaling

advanced

How does a load balancer help scale a web application?

Consider a web application experiencing increasing user traffic. How does introducing a load balancer help the system scale effectively?

A By replacing the database with a faster one automatically.

B By distributing incoming requests across multiple servers, it allows adding more servers to handle higher traffic.

C By compressing all data to reduce network usage.

D By storing user sessions on the load balancer itself.

💡 Hint

Think about how sharing work helps handle more users.

Load balancers enable horizontal scaling by distributing traffic to multiple servers, allowing the system to handle more users smoothly.

❓ tradeoff

advanced

What is a tradeoff when using load balancers?

While load balancers improve traffic distribution, what is a common tradeoff or challenge introduced by using them?

A They can become a single point of failure if not designed with redundancy.

B They reduce the total number of servers needed.

C They eliminate the need for caching in the system.

D They automatically fix all software bugs in backend servers.

💡 Hint

Think about what happens if the traffic controller stops working.

If a load balancer fails and there is no backup, the entire system can become unreachable, so redundancy is important.

❓ estimation

expert

Estimating capacity for load balancer traffic distribution

A system expects 10,000 requests per second. Each backend server can handle 2,000 requests per second. How many backend servers should the load balancer distribute traffic to, at minimum, to handle the load without overload?

A 5 servers

B 4 servers

C 6 servers

D 3 servers

💡 Hint

Divide total requests by server capacity and round up.

10,000 requests / 2,000 per server = 5 servers needed to handle the load without overload.

Practice

1. Why do load balancers distribute incoming traffic across multiple servers?

easy

A. To prevent any single server from becoming overloaded and improve system reliability

B. To increase the number of servers needed for the system

C. To slow down the response time for users

D. To reduce the total number of user requests

Solution

1. Step 1: Understand server overload

   When too many requests go to one server, it slows down or crashes.

2. Step 2: Role of load balancers

   Load balancers spread requests evenly to keep servers healthy and fast.

3. Final Answer:

   To prevent any single server from becoming overloaded and improve system reliability -> Option A

4. Quick Check:

   Load balancers prevent overload = C [OK]

Hint: Load balancers keep servers from getting too busy [OK]

Common Mistakes:

• Thinking load balancers reduce total requests
• Believing load balancers slow down responses
• Assuming load balancers increase server count unnecessarily

2. Which of the following is a common method used by load balancers to distribute traffic?

easy

A. Bubble sort

B. Binary search

C. Depth-first search

D. Round-robin

Solution

1. Step 1: Identify load balancing methods

   Common methods include round-robin and least connections.

2. Step 2: Match options to known methods

   Round-robin cycles through servers evenly; others are unrelated algorithms.

3. Final Answer:

   Round-robin -> Option D

4. Quick Check:

   Round-robin is a load balancing method = D [OK]

Hint: Round-robin cycles requests evenly [OK]

Common Mistakes:

• Confusing sorting/search algorithms with load balancing
• Choosing unrelated computer science terms
• Ignoring common load balancing strategies

3. Consider a load balancer using the least connections strategy. If Server A has 3 active connections and Server B has 1 active connection, where will the next request be sent?

medium

A. Server B

B. Server A

C. Both servers equally

D. To a new server not listed

Solution

1. Step 1: Understand least connections strategy

   It sends new requests to the server with fewer active connections.

2. Step 2: Compare active connections

   Server A has 3, Server B has 1, so Server B has fewer connections.

3. Final Answer:

   Server B -> Option A

4. Quick Check:

   Least connections picks server with fewer connections = B [OK]

Hint: Send to server with least active connections [OK]

Common Mistakes:

• Choosing server with more connections
• Assuming equal distribution regardless of load
• Thinking new servers are automatically chosen

4. A load balancer is configured to use round-robin but always sends requests to the same server. What is the most likely cause?

medium

A. The servers are all down

B. The load balancer is not tracking the last server used correctly

C. The network is too slow

D. The user requests are too few

Solution

1. Step 1: Understand round-robin behavior

   Round-robin cycles through servers in order to balance load.

2. Step 2: Identify cause of repeated server selection

   If it always picks the same server, it likely lost track of which server was last used.

3. Final Answer:

   The load balancer is not tracking the last server used correctly -> Option B

4. Quick Check:

   Round-robin needs correct tracking = A [OK]

Hint: Round-robin must remember last server used [OK]

Common Mistakes:

• Blaming server downtime without checking load balancer
• Assuming network speed affects server choice
• Thinking low request volume causes imbalance

5. You design a system with a load balancer distributing traffic to 5 servers. Suddenly, one server becomes much slower but still receives equal requests. What change to the load balancing strategy can improve overall system performance?

hard

A. Use round-robin but add more user requests

B. Increase the number of servers without changing strategy

C. Switch from round-robin to least connections to avoid slow server overload

D. Disable the load balancer and send requests to one server

Solution

1. Step 1: Identify problem with round-robin

   Round-robin sends equal requests regardless of server speed, causing slow server overload.

2. Step 2: Choose better strategy

   Least connections sends requests to less busy servers, reducing load on slow server.

3. Final Answer:

   Switch from round-robin to least connections to avoid slow server overload -> Option C

4. Quick Check:

   Least connections adapts to server speed = A [OK]

Hint: Use least connections to avoid slow servers [OK]

Common Mistakes:

• Adding servers without fixing load distribution
• Increasing requests worsens overload
• Disabling load balancer causes single point failure