Layer 4 vs Layer 7 load balancing in HLD - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Difference in Protocol Awareness

Which statement correctly describes the protocol awareness difference between Layer 4 and Layer 7 load balancers?

A Layer 4 load balancers use DNS queries for routing, and Layer 7 load balancers use MAC addresses.

B Layer 4 load balancers inspect HTTP headers to route traffic, whereas Layer 7 load balancers only use IP addresses.

C Layer 4 load balancers operate based on IP address and TCP/UDP ports without inspecting the content, while Layer 7 load balancers inspect the application data to make routing decisions.

D Layer 4 load balancers analyze the full application payload, while Layer 7 load balancers only check the TCP handshake.

💡 Hint

Think about which OSI layers correspond to IP and TCP versus application data.

Layer 4 load balancers work at the transport layer, using IP addresses and ports to forward traffic without looking at the content. Layer 7 load balancers operate at the application layer, inspecting data like HTTP headers or cookies to make smarter routing decisions.

❓ Architecture

intermediate

Choosing Load Balancer Type for a Web Application

You are designing a web application that requires routing users to different backend servers based on URL paths and user sessions. Which load balancer type should you choose?

A Layer 7 load balancer, because it can inspect HTTP headers and URLs to route requests.

B Layer 4 load balancer, because it efficiently routes based on IP and port.

C DNS load balancing, because it resolves domain names to different IPs.

D Hardware firewall, because it filters traffic based on security rules.

💡 Hint

Consider which load balancer can look inside the HTTP request to route based on URL paths.

Routing based on URL paths and user sessions requires inspecting application data, which Layer 7 load balancers can do. Layer 4 load balancers cannot inspect URLs or cookies.

❓ scaling

advanced

Scaling Impact of Layer 4 vs Layer 7 Load Balancers

Which statement best describes the scaling impact when using Layer 4 versus Layer 7 load balancers in a high-traffic environment?

A Layer 4 load balancers require more CPU resources because they decrypt SSL traffic, unlike Layer 7 load balancers.

B Layer 7 load balancers scale better because they cache all application data, reducing backend load.

C Layer 7 load balancers scale better because they operate at the network layer, which is faster.

D Layer 4 load balancers generally scale better because they perform less processing per packet compared to Layer 7 load balancers.

💡 Hint

Think about how much data each load balancer inspects and processes.

Layer 4 load balancers handle traffic based on IP and port, requiring minimal processing, so they scale well under heavy load. Layer 7 load balancers inspect application data, which is more CPU intensive and can limit scaling.

❓ tradeoff

advanced

Tradeoffs Between Layer 4 and Layer 7 Load Balancers

What is a key tradeoff when choosing between Layer 4 and Layer 7 load balancers?

A Layer 4 load balancers provide detailed content inspection but are slower; Layer 7 load balancers are faster but only route by IP.

B Layer 4 load balancers offer faster routing but less intelligent traffic management; Layer 7 load balancers provide detailed routing but with higher latency.

C Layer 4 load balancers can route based on user sessions; Layer 7 load balancers cannot.

D Layer 4 load balancers require SSL termination; Layer 7 load balancers do not.

💡 Hint

Consider speed versus intelligence in routing decisions.

Layer 4 load balancers are faster because they only look at IP and port, but they cannot make decisions based on application data. Layer 7 load balancers can route based on detailed information but add processing overhead and latency.

❓ estimation

expert

Estimating Backend Server Load with Layer 7 Load Balancer

A Layer 7 load balancer inspects HTTP headers and routes requests to backend servers. If the load balancer handles 10,000 requests per second and each inspection adds 0.1 ms processing time, estimate the total CPU time spent per second on inspection. Choose the closest value.

A 1 second of CPU time per second

B 0.1 seconds of CPU time per second

C 10 seconds of CPU time per second

D 100 seconds of CPU time per second

💡 Hint

Multiply requests per second by processing time per request.

10,000 requests/second * 0.1 ms/request = 1,000 ms = 1 second of CPU time per second.