Why scalability handles growing traffic in HLD - Quick Recap

Recall & Review

beginner

What is scalability in system design?

Scalability is the ability of a system to handle increased load or traffic by adding resources without affecting performance.

beginner

Why is scalability important for growing traffic?

Because as more users or requests come in, a scalable system can grow to meet demand, preventing slowdowns or crashes.

intermediate

Name two common ways to scale a system.

1. Vertical scaling (adding more power to one machine). 2. Horizontal scaling (adding more machines).

intermediate

How does horizontal scaling help handle growing traffic?

It spreads the load across many machines, so no single machine gets overwhelmed, improving reliability and capacity.

beginner

What can happen if a system is not scalable when traffic grows?

The system may slow down, become unresponsive, or crash because it cannot handle the extra load.

What does scalability allow a system to do?

A Handle more traffic without performance loss

B Reduce the number of users

C Make the system slower

D Limit the system to one user

Scalability means the system can handle more traffic or load without losing performance.

Which is an example of vertical scaling?

A Adding more servers to share the load

B Caching data on the client side

C Distributing traffic to multiple data centers

D Upgrading a server's CPU and RAM

Vertical scaling means making one machine more powerful, like upgrading CPU or RAM.

What is a benefit of horizontal scaling?

A Spreading load across multiple machines

B Decreasing system capacity

C Single point of failure

D Reducing network bandwidth

Horizontal scaling spreads the load across many machines, improving capacity and reliability.

If traffic grows but the system is not scalable, what is likely to happen?

A Traffic decreases automatically

B System performance improves

C System crashes or slows down

D Users get faster responses

Without scalability, increased traffic can cause slowdowns or crashes.

Which of these is NOT a way to improve scalability?

A Optimizing code

B Ignoring traffic growth

C Adding more servers

D Using load balancers

Ignoring traffic growth does not improve scalability; it causes problems.

Explain in simple terms why scalability is important when traffic grows.

Think about a busy store and how it needs more cashiers when more customers come.

Describe the difference between vertical and horizontal scaling and how each helps with growing traffic.

Imagine upgrading one car vs adding more cars to carry more people.

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