DBS-C01 Vertical scaling Practice Question
A company's RDS for MySQL instance is experiencing high CPU utilization. Which AWS service should be used to set up automated actions to scale the instance vertically?
⚠ Common exam trap
The trap is that candidates assume AWS Auto Scaling handles both horizontal and vertical scaling for RDS, but it only supports horizontal scaling (adding/removing replicas). Vertical scaling (changing instance class) requires a custom automation, such as a Lambda function triggered by CloudWatch Alarms.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
AWS Lambda function to modify the DB instance class
For automated vertical scaling of an RDS for MySQL instance, the most direct approach among the options is to use an AWS Lambda function that modifies the DB instance class, triggered by a CloudWatch alarm based on CPU utilization. AWS Auto Scaling (B) only supports horizontal scaling for RDS (adding read replicas) and does not natively change instance class. Systems Manager Automation (A) could orchestrate a change but is less straightforward than Lambda. CloudWatch Alarms (D) only notify; they cannot automatically scale without an action target like Lambda. Therefore, option C is the best choice.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
AWS Systems Manager Automation with a custom runbook
Why it's wrong here
AWS Systems Manager Automation can automate tasks, but it is less commonly used for direct RDS instance class modifications compared to Lambda. It is not the most direct method.
- ✗
AWS Auto Scaling with a target tracking scaling policy
Why it's wrong here
AWS Auto Scaling with a target tracking scaling policy is designed for horizontal scaling (adding/removing read replicas). It does not support vertical scaling (changing the DB instance class) for RDS.
- ✓
AWS Lambda function to modify the DB instance class
Why this is correct
An AWS Lambda function can be triggered by a CloudWatch alarm to call the RDS modify-db-instance API and change the instance class, enabling automated vertical scaling.
- ✗
Amazon CloudWatch Alarms to send an SNS notification to the DBA
Why it's wrong here
CloudWatch Alarms can send SNS notifications, but they cannot directly modify the RDS instance. They require an action target (like Lambda) to perform the scaling.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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