Concepts
When it comes to cloud computing and, more specifically, preparing for the AWS Certified Solutions Architect – Associate exam, understanding the concepts of horizontal scaling and vertical scaling is crucial. These two strategies are used to handle increasing workloads and to ensure that applications can effectively and efficiently serve user requests.
Vertical Scaling (Scaling Up and Down)
Vertical scaling, also known as “scaling up” or “scaling down,” refers to the process of adding or removing resources to a single instance in a system. In the context of AWS, this could involve changing the size of an EC2 instance to a larger or smaller type, which can be done without deploying new instances. When you scale up, you are upgrading to an instance with more capacity – for example, from a t2.small to a t3.large. Conversely, scaling down is the process of moving to an instance with less capacity, potentially to save costs during off-peak times.
Vertical scaling is suitable for workloads that are not distributed by nature or that have limitations on horizontal scaling. It’s often the simplest way to get more power, as it does not require any changes to the application code. However, vertical scaling has its limits, as there is a maximum size an individual instance or server can reach before you must consider an alternative scaling approach.
Horizontal Scaling (Scaling Out and In)
Horizontal scaling, conversely, is known as “scaling out” or “scaling in.” Rather than changing the capabilities of an individual instance, horizontal scaling adds or removes instances altogether within a cluster or a distributed computing environment. In AWS terms, this can be done by adjusting the number of EC2 instances within an Auto Scaling group.
Scaling out is used when there is a need to handle more concurrent users or services. You can distribute the load across multiple instances to ensure that a single instance doesn’t become a bottleneck. Scaling in is the process of removing instances to save costs when the extra capacity is no longer needed.
A prime example of horizontal scaling on AWS is the Elastic Load Balancer (ELB) distributing traffic across multiple EC2 instances. This set up ensures high availability and fault tolerance.
Comparing Horizontal and Vertical Scaling
Here is a comparison table to clarify the key differences between horizontal scaling and vertical scaling:
| Feature | Horizontal Scaling (Out/In) | Vertical Scaling (Up/Down) |
|---|---|---|
| Resource Adjustment | Adding/removing instances | Changing the size of existing instances |
| Downtime | Usually none, as new instances can be added while the system is running | Possible downtime during instance resizing |
| Cost | Can be cost-effective by closely matching resources to load, but may require a more complex setup | Simple to implement, but may reach a point where it is no longer cost-effective as the instance size grows |
| Limitations | More complex, requires applications to be designed for distribution | Limited by the maximum capacity of a single instance |
| AWS Services | EC2 Auto Scaling, ELB | EC2, EBS |
| Fault Tolerance | Increased, as the system can survive instance failures | Decreased, as the system relies on a single instance |
| Scalability | Virtually unlimited, can scale out to as many instances as required | Limited to the size of the largest available instance type |
Implementing Scaling on AWS
On AWS, you can implement horizontal scaling with services like Auto Scaling Groups, which automatically adjust the number of EC2 instances in response to traffic demands. Below is a high-level example of how to create an Auto Scaling group with an attached load balancer:
- Create a launch configuration that specifies the EC2 instance type and AMI.
- Define an Auto Scaling group by setting minimum, desired, and maximum numbers of instances.
- Attach one or more scaling policies that determine when and how to scale out or scale in (based on metrics like CPU utilization).
- Associate an Elastic Load Balancer to distribute incoming traffic across the instances in the Auto Scaling group.
Vertical scaling can be achieved by simply changing the instance type of your existing EC2 instance, which can be performed via the AWS Management Console, AWS CLI, or AWS SDKs.
Conclusion
Both horizontal and vertical scaling have their places in a cloud architect’s toolbox, and a well-designed system may use a combination of both to take advantage of the strengths of each method while mitigating their limitations. Understanding these concepts and how to apply them within AWS is fundamental for those aiming to become AWS Certified Solutions Architects.
Answer the Questions in Comment Section
True or False: Horizontal scaling involves adding more machines to a pool of resources, while vertical scaling involves adding more power (CPU, RAM) to an existing machine.
- A) True
- B) False
Answer: A) True
Explanation: Horizontal scaling refers to adding more instances of the same type to handle the load, whereas vertical scaling refers to increasing the resources of an existing instance.
Which AWS service is typically associated with vertical scaling?
- A) Amazon EC2
- B) Amazon S3
- C) Amazon DynamoDB
- D) AWS Lambda
Answer: A) Amazon EC2
Explanation: Amazon EC2 instances can be scaled vertically by changing the instance type to a more powerful one.
True or False: Horizontal scaling is generally considered to be more fault-tolerant than vertical scaling.
- A) True
- B) False
Answer: A) True
Explanation: Horizontal scaling provides fault tolerance by distributing the load across multiple instances, which can help prevent a single point of failure.
Which of the following is an example of horizontal scaling in AWS?
- A) Switching to a higher-capacity instance type
- B) Adding read replicas in Amazon RDS
- C) Increasing the size of an EBS volume
- D) Upgrading an instance’s CPU
Answer: B) Adding read replicas in Amazon RDS
Explanation: Adding read replicas in Amazon RDS is an example of horizontal scaling because it involves adding additional database instances to handle more traffic.
True or False: Auto Scaling is an AWS service that aids both horizontal and vertical scaling.
- A) True
- B) False
Answer: B) False
Explanation: Auto Scaling in AWS is predominantly used for horizontal scaling by automatically adapting the number of instances to the changing demand.
When should you consider vertical scaling over horizontal scaling?
- A) When the application has monolithic architecture
- B) When data consistency is not a priority
- C) When low-latency read replicas are required
- D) When the application is stateless
Answer: A) When the application has monolithic architecture
Explanation: Monolithic applications might benefit more from vertical scaling since they are often designed to run on a single server with a single data store.
What is a disadvantage of vertical scaling?
- A) Increased management complexity
- B) Limited capacity based on the size of the largest server
- C) The necessity to distribute traffic across instances
- D) Potential service interruptions during scaling operations
Answer: B) Limited capacity based on the size of the largest server
Explanation: The main disadvantage of vertical scaling is the limitation imposed by the maximum capacity of a single server.
In AWS, which feature enables automatic horizontal scaling of Amazon EC2 instances?
- A) Elastic Load Balancing
- B) EC2 Auto Scaling
- C) AWS Lambda
- D) Amazon S3
Answer: B) EC2 Auto Scaling
Explanation: EC2 Auto Scaling automatically adjusts the number of EC2 instances in response to changes in demand to maintain performance and reduce costs.
True or False: Vertical scaling typically results in zero downtime.
- A) True
- B) False
Answer: B) False
Explanation: Vertical scaling often involves hardware upgrades or changing the instance type, which can result in downtime as the system is restarted or migrated.
Which AWS service allows you to distribute load horizontally across multiple targets, such as EC2 instances?
- A) Amazon RDS
- B) AWS Lambda
- C) Elastic Load Balancing
- D) AWS Elastic Beanstalk
Answer: C) Elastic Load Balancing
Explanation: Elastic Load Balancing distributes incoming application traffic across multiple targets, such as Amazon EC2 instances, enabling horizontal scaling.
True or False: Vertical scaling is generally less expensive than horizontal scaling in the long run.
- A) True
- B) False
Answer: B) False
Explanation: Vertical scaling can become more expensive as there is a physical limit to how much you can scale a single resource, and the cost of high-capacity servers tends to rise significantly.
What is one of the benefits of horizontal scaling?
- A) Single point of failure
- B) Better resource utilization
- C) Simplicity in management
- D) Easy to implement with legacy systems
Answer: B) Better resource utilization
Explanation: Horizontal scaling can lead to better resource utilization as you can scale out to exactly meet demand, and unused resources can be shut down to save costs.
Great post! Horizontal scaling and vertical scaling are always confusing for me. This cleared up a lot!
For horizontal scaling in AWS, are we mostly talking about adding more EC2 instances?
How do you decide between horizontal and vertical scaling for a web application?
This blog post is fantastic. Cleared up so many questions I had!
Is there a limit to vertical scaling in AWS?
Can anyone explain how auto-scaling works in AWS?
Horizontal scaling seems more reliable than vertical scaling in terms of fault tolerance. Any thoughts?
Thanks for the insightful post!