Improving Application Reliability with Auto Scaling and Aurora

SAP-C02 By islever Editorial Last updated

Design reliable and resilient architectures.

Short answer

AC Implement Auto Scaling with ALB for the web tier, migrate to Aurora for the database tier, and add a second public subnet for cross-AZ availability.

Question

A company runs an application in the cloud that consists of a database and a website. Users can post data to the website, have the data processed, and have the data sent back to them in an email. Data is stored in a MySQL database running on an Amazon EC2 instance. The database is running in a VPC with two private subnets. The website is running on Apache Tomcat in a single EC2 instance in a different VPC with one public subnet. There is a single VPC peering connection between the database and website VPC. The website has suffered several outages during the last month due to high traffic. Which actions should a solutions architect take to increase the reliability of the application? (Choose three.)
  1. Place the Tomcat server in an Auto Scaling group with multiple EC2 instances behind an Application Load Balancer. Correct Answer
  2. Provision an additional VPC peering connection.
  3. Migrate the MySQL database to Amazon Aurora with one Aurora Replica. Correct Answer
  4. Provision two NAT gateways in the database VPC.
  5. Move the Tomcat server to the database VPC.

Key Takeaways

The exam tests your ability to identify Single Points of Failure (SPOFs) in a VPC-peered architecture and apply AWS best practices like Auto Scaling Groups, Load Balancers, and Multi-AZ database replicas to ensure reliability.

This question addresses designing a reliable architecture for a web application by eliminating single points of failure in both the compute layer (Tomcat) and the data layer (MySQL). The correct solution involves implementing high availability through redundancy and managed services.

Common mistake: Many candidates choose AC but miss F because they overlook that a single public subnet is not highly available. Others incorrectly select B or D, failing to realize that additional peering connections or NAT gateways do not address the core availability issues of the EC2 instances.

Expert Analysis

Why the Answer Is Correct

To increase reliability, you must remove single points of failure. Option A creates redundancy for the web tier by using an Auto Scaling Group behind an Application Load Balancer, ensuring the site stays up during traffic spikes or instance failures. Option C migrates the database to Amazon Aurora, which provides built-in multi-AZ replication and self-healing storage, significantly improving data availability compared to a single EC2-hosted MySQL instance. Although Option F is not listed in the provided options text, community comments and the standard pattern for this specific exam question confirm that 'Create an additional public subnet in a different Availability Zone' is the third required action to ensure the website tier has cross-AZ resilience.

Why the Other Options Are Wrong

Option B is incorrect because adding another VPC peering connection does not increase availability; it only adds routing paths, and peering connections are not inherently redundant across AZs unless configured specifically, which isn't stated. Option D is incorrect because NAT gateways handle outbound internet access for private subnets; adding more does not help the reliability of the inbound web traffic or the database availability. Option E is incorrect and technically flawed because you cannot simply move an EC2 instance to another VPC without re-creating it, and moving the web server into the database VPC (which has no public subnets) would make it inaccessible without complex NAT configurations.

Community Comment Notes

Community consensus strongly supports ACF as the correct combination. As user kejam noted, 'These increase reliability of the app,' highlighting that A, C, and F directly address SPOFs. User HunkyBunky correctly identified that moving the Tomcat server to the database VPC (Option E) is invalid because that VPC lacks public subnets. Multiple users confirmed that B and D provide no benefit to the reliability of the application stack itself.

Exam Strategy

When asked about reliability, always look for 'redundancy' and 'multiple Availability Zones'. If you see a single EC2 instance handling web traffic, think Auto Scaling + Load Balancer. If you see a database on EC2, think RDS/Aurora with Multi-AZ. Avoid options that just add capacity (like more NAT gateways) unless specifically needed for throughput, not availability.

Frequently Asked Questions

Why is adding a second VPC peering connection (B) wrong for reliability?

VPC peering is not a high-availability mechanism. It connects two VPCs but does not provide redundancy against AZ failures or instance crashes within those VPCs.

Can I move an existing EC2 instance to another VPC easily?

No. You cannot directly move a running EC2 instance to a different VPC. You must create a new instance in the target VPC from a snapshot or AMI, which disrupts service.

More SAP-C02 FAQ →

Discussion 7 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 7

  1. kejam 👍 7
    Answer: ACF These increase reliability of the app. F. Create an additional public subnet in a different Availability Zone in the website VPC. A. Place the Tomcat server in an Auto Scaling group with multiple EC2 instances behind an Application Load Balancer. C. Migrate the MySQL database to Amazon Aurora with one Aurora Replica. These do not. B. Provision an additional VPC peering connection. D. Provision two NAT gateways in the database VPC. E. Move the Tomcat server to the database VPC. (good idea for security, but we're after reliability)
  2. HunkyBunky 👍 2
    B - not correct, because will not give us any benefit D - not correct, because will not give us any benefit E - looks not correct, because if we move website into database VPC - this VPC don't contains any public subnet, so it will be inaccessible
  3. sat2008 👍 2
    You cant move Ec2 directly to another VPC need to migrate between VPCs
  4. AzureDP900 👍 1
    ACF These three options improve the reliability and scalability of the application by: Reducing the likelihood of single points of failure Improving data availability and durability Providing an additional layer of redundancy
  5. alexis123456 👍 4
    correct answer is ACF
Show 2 more comments
  1. arberod 👍 2
    agree ACF
  2. career360guru 👍 1
    Option A, C, F

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