In the technological sphere, scalability is an essential feature of any infrastructure to meet the requirement of an increasing workload. Scalability ensures a system’s ability to handle a growing amount of work or its potential to accommodate growth. It falls under two categories associated with the AWS Certified Solutions Architect- Associate: horizontal scaling and vertical scaling.

Table of Contents

Horizontal Scaling (Scaling Out)

Horizontal scaling implies a system can increase its size by adding more nodes into the existing pool. This means that you are expanding your system by connecting several software or hardware entities so that they function as a single logical unit. It’s like adding more machines into your existing resources, thereby distributing the load evenly across the network. AWS Elastic Load Balancing service is a great example where horizontal scaling is implemented.

For example, when the need for more computational resources arises in a routine AWS EC2 deployment, you can simply add more instances with required configurations to your current fleet of running instances to bring down the load on the overall system. This action can be performed either manually or by implementing Auto Scaling Group that decides when and how many additional instances are needed based on certain policies.

Vertical Scaling (Scaling Up)

On the other hand, vertical scaling involves increasing the capacity of a single node within the system, such as processing power or memory. In other words, you are enhancing the resources of an existing machine, such as increasing the RAM in your machine from 4 GB to 8 GB. This mainly involves upgrading the machine’s hardware or software components. Using an AWS-specific example, vertical scaling could be seen when you change the instance type of your EC2 machine to handle more load or increase efficiency.

For instance, if you have an EC2 instance of type t2.micro that is running hot, you can easily upgrade (scale up) the instance to a higher variant like t2.large which offers more CPU power, better I/O performance and higher memory. This action of increasing resources can be performed manually or through automation with the help of AWS EC2 Auto Scaling which changes the instance type based on given policies.

Comparative Difference

Horizontal Scaling (scaling out) Vertical Scaling (scaling up)
Add more systems into the pool of resources Boosts capability of existing hardware or software
High cost-effective strategy Rapidly becomes expensive as higher performance systems cost much more
Failures are better isolated and affects limited users Any outage can affect the performance of the entire application
Can be easily done with commodity hardware Might involve downtime for application or the system


The method you choose depends on the application or workload that you are going to scale. Horizontal scaling better suits applications and workloads that need to serve a larger volume of lighter requests, while vertical scaling can be ideal for applications and workloads that require heavy computational power on single nodes. AWS provides flexible options for both horizontal and vertical scaling to make the best use of resources and provide the optimal user experience in your applications.

Practice Test

True or False: Horizontal Scaling involves adding more hardware to an existing system to improve its ability to manage higher load.

  • False

Correct Answer: False

Explanation: Horizontal scaling involves adding more machines or servers into the pool to manage higher load, not adding more hardware to an existing system.

True or False: Vertical scaling is also known as scale-out.

  • False

Correct Answer: False

Explanation: Vertical scaling is also known as scale-up, not scale-out. Horizontal scaling is known as scale-out.

In which scaling model is data consistency easier to achieve?

  • Vertical scaling
  • Horizontal scaling
  • Both
  • None of the above

Correct Answer: Vertical scaling

Explanation: In vertical scaling, data consistency is easier to achieve because the requests are being processed on a single machine and distributed transactions aren’t required.

True or False: AWS EC2 provides support for both horizontal and vertical scaling.

  • True

Correct Answer: True

Explanation: AWS EC2 indeed supports both horizontal and vertical scaling. You can increase the instance size (vertical) or increase the number of instances (horizontal).

Which AWS service is typically used to achieve horizontal scaling?

  • AWS EC2
  • AWS Lambda
  • AWS Elastic Beanstalk
  • AWS Autoscaling

Correct Answer: AWS Autoscaling

Explanation: AWS Autoscaling is typically used to automate the process of horizontal scaling by adjusting the number of EC2 instances in response to the load.

Vertical scaling typically poses a higher risk of single point of failure.

  • True
  • False

Correct Answer: True

Explanation: Vertical Scaling typically poses higher risks of single point of failure as it depends on a single system.

In terms of cost, horizontal scaling is typically more expensive than vertical scaling.

  • True
  • False

Correct Answer: False

Explanation: Horizontal scaling can be more cost-effective as it uses lower-cost commodity hardware, unlike vertical scaling which requires high-end hardware as resources are scaled up.

True or False: Vertical scaling requires applications to have the ability to span multiple servers.

  • False

Correct Answer: False

Explanation: Vertical scaling doesn’t require applications to span multiple servers as it involves increasing the capacity of a single server. Horizontally scaling is what involves spanning multiple servers.

True or False: Distributing the load across multiple servers is a characteristic of horizontal scaling.

  • True

Correct Answer: True

Explanation: In horizontal scaling, you distribute the load across multiple servers which is why it’s also known as scale-out.

Which scaling approach is more environmentally friendly due to the efficient use of energy?

  • Horizontal Scaling
  • Vertical Scaling
  • Both
  • None

Correct Answer: Horizontal Scaling

Explanation: Horizontal scaling is more energy-efficient and environmentally-friendly as it spreads out the load, thus using less energy compared to vertical scaling which relies on larger, more powerful and less energy-efficient servers.

Interview Questions

What is horizontal scaling in cloud computing?

Horizontal scaling, also known as scale-out, involves adding more servers or instances to your server pool to spread the load and handle increased capacity.

What is the vertical scaling in the context of AWS?

Vertical scaling, also known as scale-up, is the process of adding more resources such as CPU, Memory or storage to an existing server or replacing the server with a more powerful one.

How does AWS support horizontal scaling?

AWS supports horizontal scaling through services like Auto Scaling and Elastic Load Balancing. Auto Scaling allows you to automatically adjust the number of EC2 instances in response to traffic demand while Elastic Load Balancing distributes incoming traffic across multiple instances.

Which AWS service would you choose for vertical scaling?

Amazon RDS (Relational Database Service) supports vertical scaling. You can switch your database instance for a larger type to get more CPU, Memory, IO, and storage.

In which scenarios should you consider vertical scaling?

Vertical scaling is often considered in scenarios where application compatibility or latency are the main concerns, and the application doesn’t support clustering or distributed computing.

What is a main benefit of horizontal scaling?

A main benefit of horizontal scaling is that it provides a high degree of flexibility, allowing you to quickly add more resources to your system as required to handle increased load.

What is one potential drawback of vertical scaling?

One potential drawback of vertical scaling is the physical limit of a single machine. After that limit is reached, the service will not be able to handle additional load.

What AWS service can automatically increase or decrease your instances based on conditions defined?

Amazon EC2 Auto Scaling service can automatically increase or decrease your instances based on defined conditions.

Which AWS service helps in achieving horizontal scalability by distributing the load amongst several resources?

AWS Elastic Load Balancer helps in achieving horizontal scalability by distributing the load amongst several resources.

Does vertical scaling require any downtime?

Yes, vertical scaling typically requires distractions in services or planned downtime because it often requires a system to be shut down or rebooted to upgrade the hardware.

In which scaling method are you more likely to face a single point of failure risk?

Vertical scaling is more likely to face a single point of failure risk because it relies on a single, large machine for operations.

Can both horizontal and vertical scaling be combined?

Yes, in AWS both horizontal and vertical scaling can be combined to achieve an optimal performance and cost balance.

Is Amazon Redshift designed for horizontal or vertical scaling?

Amazon Redshift is designed for horizontal scalability, enabling you to add more nodes to your data warehouse cluster as you add more data.

Which scaling approach, horizontal or vertical, is more cost-effective in AWS?

Horizontal scaling is generally more cost-effective than vertical scaling in AWS because it leverages smaller, less expensive resources to achieve the same or higher level of performance.

How does Amazon DynamoDB support horizontal scaling?

Amazon DynamoDB supports horizontal scaling through partitioning, where data is spread across multiple partitions by using a partition key. You can also use DynamoDB auto scaling to automatically adjust provisioned throughput capacity in response to actual traffic patterns.

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