Why scalability handles growing traffic in HLD - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

How does horizontal scaling improve system capacity?

Imagine a busy restaurant that adds more tables to serve more customers at the same time. How does this relate to horizontal scaling in system design?

A By adding more servers to share the load, allowing more requests to be handled simultaneously.

B By upgrading the CPU and memory of a single server to handle more requests.

C By reducing the number of users accessing the system to prevent overload.

D By storing all data in a single large database to speed up access.

💡 Hint

Think about adding more workers versus making one worker stronger.

Horizontal scaling means adding more servers (like adding tables) to handle more users at once. This spreads the load and improves capacity.

❓ Architecture

intermediate

Which component helps distribute traffic evenly in a scalable system?

In a system designed to handle growing traffic, which component ensures that incoming requests are shared fairly among multiple servers?

A Load balancer

B Firewall

C Cache server

D Database

💡 Hint

Think about a traffic cop directing cars to different lanes.

A load balancer distributes incoming requests evenly across servers to prevent any single server from becoming overwhelmed.

❓ scaling

advanced

What is a key tradeoff when scaling vertically to handle more traffic?

Vertical scaling means upgrading a single server's resources. What is a main limitation or tradeoff of this approach?

A It automatically distributes traffic evenly across servers.

B It can become very expensive and has physical limits on hardware upgrades.

C It requires adding more servers to the system.

D It eliminates the need for a database.

💡 Hint

Think about how much you can upgrade one computer before it stops improving.

Vertical scaling improves a single server's power but is limited by hardware capacity and cost, unlike horizontal scaling which adds more servers.

❓ estimation

advanced

Estimate the number of servers needed to handle 10,000 requests per second if one server handles 1,000 requests per second.

If each server can handle 1,000 requests per second, how many servers are needed to handle 10,000 requests per second assuming even load distribution?

A 5 servers

B 1 server

C 100 servers

D 10 servers

💡 Hint

Divide total requests by requests per server.

To handle 10,000 requests per second with each server handling 1,000, you need 10 servers (10,000 ÷ 1,000 = 10).

❓ tradeoff

expert

What is a major challenge when scaling a system horizontally with many servers?

When adding many servers to handle growing traffic, what is a common challenge that can affect system performance?

A Reducing the number of users accessing the system.

B Upgrading the CPU of a single server.

C Ensuring data consistency and synchronization across servers.

D Storing all data on one server to simplify access.

💡 Hint

Think about how multiple workers keep their work aligned.

Horizontal scaling adds complexity in keeping data consistent and synchronized across many servers, which can impact performance and reliability.

Practice

1. What does scalability in system design primarily help with?

easy

A. Handling more users and traffic smoothly

B. Reducing the number of servers

C. Making the system slower

D. Limiting the system to one user

Solution

1. Step 1: Understand the meaning of scalability

   Scalability means the system can grow to handle more users or traffic without problems.

2. Step 2: Identify the main goal of scalability

   The main goal is to manage increasing traffic smoothly, not to reduce servers or slow down.

3. Final Answer:

   Handling more users and traffic smoothly -> Option A

4. Quick Check:

   Scalability = Handling more traffic [OK]

Hint: Scalability means growing capacity to handle more users [OK]

Common Mistakes:

• Thinking scalability reduces servers
• Confusing scalability with slowing system
• Believing scalability limits users

2. Which option correctly describes vertical scaling?

easy

A. Upgrading the hardware of a single machine

B. Distributing traffic using load balancers

C. Adding more machines to the system

D. Reducing the number of users

Solution

1. Step 1: Define vertical scaling

   Vertical scaling means improving one machine's hardware, like adding CPU or memory.

2. Step 2: Differentiate from other options

   Adding machines is horizontal scaling; load balancers distribute traffic; reducing users is unrelated.

3. Final Answer:

   Upgrading the hardware of a single machine -> Option A

4. Quick Check:

   Vertical scaling = Upgrade one machine [OK]

Hint: Vertical scaling upgrades one machine's hardware [OK]

Common Mistakes:

• Confusing vertical with horizontal scaling
• Thinking vertical scaling adds machines
• Mixing load balancers with scaling types

3. Consider a system with 3 servers behind a load balancer. If traffic doubles, what happens when horizontal scaling is applied?

medium

A. Remove servers to reduce complexity

B. Upgrade the CPU of one server only

C. Add more servers to share the load

D. Ignore traffic increase and keep same setup

Solution

1. Step 1: Understand horizontal scaling

   Horizontal scaling means adding more servers to handle increased traffic.

2. Step 2: Apply to the scenario

   With doubled traffic, adding servers helps share load; upgrading one server is vertical scaling.

3. Final Answer:

   Add more servers to share the load -> Option C

4. Quick Check:

   Horizontal scaling = Add servers [OK]

Hint: Horizontal scaling means adding servers [OK]

Common Mistakes:

• Choosing to upgrade one server (vertical scaling)
• Removing servers when traffic grows
• Ignoring traffic increase

4. A system uses a load balancer but still crashes under high traffic. What is the likely issue?

medium

A. Too many servers are added unnecessarily

B. Load balancer is not distributing traffic evenly

C. Vertical scaling was applied correctly

D. Traffic is decreasing, causing overload

Solution

1. Step 1: Analyze load balancer role

   Load balancers distribute traffic evenly to servers to prevent overload.

2. Step 2: Identify cause of crash

   If system crashes despite load balancer, it may not be distributing traffic properly, causing some servers to overload.

3. Final Answer:

   Load balancer is not distributing traffic evenly -> Option B

4. Quick Check:

   Uneven load distribution causes crashes [OK]

Hint: Check if load balancer spreads traffic evenly [OK]

Common Mistakes:

• Assuming too many servers cause crash
• Thinking vertical scaling always fixes crashes
• Believing traffic decrease causes overload

5. A web app faces sudden traffic spikes. Which combination best ensures smooth scaling?

hard

A. Only upgrade one server's CPU and RAM

B. Limit user access to reduce traffic

C. Remove load balancers and rely on a single powerful server

D. Use horizontal scaling with load balancers and auto-scaling groups

Solution

1. Step 1: Identify best scaling approach for spikes

   Horizontal scaling with load balancers allows adding/removing servers dynamically to handle spikes.

2. Step 2: Evaluate other options

   Upgrading one server limits capacity; removing load balancers causes bottlenecks; limiting users reduces usability.

3. Final Answer:

   Use horizontal scaling with load balancers and auto-scaling groups -> Option D

4. Quick Check:

   Horizontal scaling + load balancers = smooth spikes [OK]

Hint: Combine horizontal scaling and load balancers for spikes [OK]

Common Mistakes:

• Relying only on vertical scaling
• Removing load balancers causing bottlenecks
• Limiting users instead of scaling