Vertical scaling vs horizontal scaling in HLD - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding vertical scaling benefits

Which of the following is a primary benefit of vertical scaling in system design?

A It automatically replicates data across different geographic regions.

B It distributes load across multiple machines to increase fault tolerance.

C It allows adding more powerful resources to a single machine to improve performance.

D It reduces the need for load balancers by using multiple servers.

💡 Hint

Think about what happens when you upgrade a single server's CPU or RAM.

Vertical scaling means upgrading the capacity of one machine, such as adding more CPU or memory, to improve performance.

❓ Architecture

intermediate

Choosing horizontal scaling for fault tolerance

In which scenario is horizontal scaling more advantageous than vertical scaling?

A When you want to increase system availability by adding multiple servers.

B When upgrading a single server's CPU is cheaper than buying new servers.

C When the system has low traffic and minimal load.

D When the application requires a single powerful database instance.

💡 Hint

Consider how spreading load across machines affects uptime.

Horizontal scaling adds more machines to share the load, improving fault tolerance and availability.

❓ scaling

advanced

Scaling tradeoffs in database systems

What is a common tradeoff when choosing horizontal scaling over vertical scaling for a database system?

A Horizontal scaling can increase complexity due to data consistency challenges.

B Vertical scaling makes it easier to distribute data across regions.

C Vertical scaling requires more network bandwidth than horizontal scaling.

D Horizontal scaling always reduces latency compared to vertical scaling.

💡 Hint

Think about how data is managed across multiple machines.

Horizontal scaling often introduces complexity in keeping data consistent across servers.

❓ estimation

advanced

Estimating capacity with horizontal scaling

If a single server can handle 1000 requests per second, how many servers are needed to handle 10,000 requests per second using horizontal scaling?

A 100 servers to ensure redundancy

B 1 server upgraded 10 times

C 5 servers with double capacity each

D 10 servers

💡 Hint

Divide total requests by capacity per server.

To handle 10,000 requests with servers each handling 1,000, you need 10 servers.

❓ tradeoff

expert

Choosing scaling strategy for a global web application

For a global web application requiring low latency worldwide and high availability, which scaling approach is best?

A Vertical scaling by upgrading a central server to the highest capacity.

B Horizontal scaling with distributed servers across regions and load balancing.

C Vertical scaling combined with a single regional data center.

D No scaling, relying on caching only.

💡 Hint

Consider geographic distribution and fault tolerance.

Distributing servers globally with horizontal scaling reduces latency and improves availability.

Practice

1. Which of the following best describes vertical scaling in system design?

easy

A. Using caching to speed up data access

B. Adding more machines to distribute the workload

C. Splitting data across multiple databases

D. Adding more resources like CPU or RAM to a single machine

Solution

1. Step 1: Understand vertical scaling definition

   Vertical scaling means improving one machine's capacity by adding resources like CPU, RAM, or storage.

2. Step 2: Compare with other options

   Options B and C describe horizontal scaling or data partitioning, and D is about caching, not scaling.

3. Final Answer:

   Adding more resources like CPU or RAM to a single machine -> Option D

4. Quick Check:

   Vertical scaling = adding resources to one machine [OK]

Hint: Vertical scaling = beef up one machine, not add machines [OK]

Common Mistakes:

• Confusing vertical scaling with horizontal scaling
• Thinking adding machines is vertical scaling
• Mixing caching with scaling

2. Which option correctly shows horizontal scaling in a system architecture?

easy

A. Adding multiple servers behind a load balancer

B. Upgrading the CPU and RAM of a single server

C. Increasing the disk size of one database server

D. Using a faster network switch

Solution

1. Step 1: Identify horizontal scaling characteristics

   Horizontal scaling means adding more machines to share the workload, often managed by a load balancer.

2. Step 2: Eliminate other options

   Options B and C describe vertical scaling (upgrading one machine), and D is about network hardware, not scaling.

3. Final Answer:

   Adding multiple servers behind a load balancer -> Option A

4. Quick Check:

   Horizontal scaling = add machines behind load balancer [OK]

Hint: Horizontal scaling = add servers, vertical = upgrade one [OK]

Common Mistakes:

• Choosing upgrading one server as horizontal scaling
• Confusing network upgrades with scaling
• Ignoring load balancer role

3. Consider a web application initially running on a single server with 8 CPU cores and 16GB RAM. If the traffic doubles, which scaling approach will likely double the capacity most efficiently?

medium

A. Upgrade the server to 16 CPU cores and 32GB RAM (vertical scaling)

B. Add one more identical server and use a load balancer (horizontal scaling)

C. Add caching layer without changing servers

D. Increase database storage size

Solution

1. Step 1: Analyze capacity needs for doubled traffic

   Doubling traffic usually requires doubling processing power or distributing load.

2. Step 2: Compare vertical vs horizontal scaling efficiency

   Vertical scaling (Upgrade the server to 16 CPU cores and 32GB RAM (vertical scaling)) can be costly and limited by hardware max. Horizontal scaling (Add one more identical server and use a load balancer (horizontal scaling)) adds another server to share load, often more efficient and scalable.

3. Final Answer:

   Add one more identical server and use a load balancer (horizontal scaling) -> Option B

4. Quick Check:

   Doubling capacity = add server (horizontal) better than upgrade [OK]

Hint: Doubling load? Add servers horizontally, not just upgrade one [OK]

Common Mistakes:

• Assuming vertical scaling always doubles capacity easily
• Ignoring load balancer role in horizontal scaling
• Confusing storage increase with processing capacity

4. A system uses vertical scaling by upgrading a server's CPU and RAM. After some time, the server crashes under load. What is the most likely cause?

medium

A. The server reached hardware limits and cannot scale further vertically

B. The load balancer is misconfigured

C. The database storage is full

D. The network bandwidth is too high

Solution

1. Step 1: Understand vertical scaling limits

   Vertical scaling improves one machine but has physical hardware limits beyond which it cannot handle more load.

2. Step 2: Analyze crash cause

   Since the server crashes under load after upgrades, it likely hit max capacity. Other options relate to load balancer, storage, or network, which are less likely causes here.

3. Final Answer:

   The server reached hardware limits and cannot scale further vertically -> Option A

4. Quick Check:

   Vertical scaling hits hardware limits causing crashes [OK]

Hint: Vertical scaling hits max hardware limits causing failures [OK]

Common Mistakes:

• Blaming load balancer when none is used
• Confusing storage issues with CPU/RAM limits
• Ignoring hardware capacity limits

5. A startup expects rapid user growth and unpredictable traffic spikes. They want a scalable system with minimal downtime and cost efficiency. Which scaling strategy should they prioritize?

hard

A. Vertical scaling by upgrading a powerful single server

B. Relying on manual server upgrades during peak times

C. Horizontal scaling with multiple servers and auto-scaling

D. Using a single server with a large database

Solution

1. Step 1: Identify startup needs

   Rapid growth and unpredictable spikes require flexible, scalable solutions that can adjust resources quickly without downtime.

2. Step 2: Evaluate scaling options for flexibility and cost

   Vertical scaling (Vertical scaling by upgrading a powerful single server) is limited and costly for spikes. Manual upgrades (Relying on manual server upgrades during peak times) cause downtime and delay. Single server (Using a single server with a large database) risks failure. Horizontal scaling with auto-scaling (Horizontal scaling with multiple servers and auto-scaling) adds/removes servers dynamically, balancing cost and uptime.

3. Final Answer:

   Horizontal scaling with multiple servers and auto-scaling -> Option C

4. Quick Check:

   Rapid growth needs horizontal auto-scaling for cost and uptime [OK]

Hint: Rapid growth? Use horizontal auto-scaling for flexibility [OK]

Common Mistakes:

• Choosing vertical scaling for unpredictable spikes
• Ignoring downtime caused by manual upgrades
• Relying on single server risking failure