AWS Certified Solutions Architect High Availability and Scalability 3 — Questions and Answers
Question 1: A company wants to run a stateless web tier that scales to zero when there is no traffic. Which AWS service best achieves this with the lowest operational overhead?
- EC2 Auto Scaling with a minimum of 0 instances
- AWS Fargate with ECS Service Auto Scaling
- AWS Lambda with API Gateway (Correct answer)
- Elastic Beanstalk with environment scaling
Correct answer: AWS Lambda with API Gateway
Lambda scales to zero automatically and only runs when invoked, making it ideal for workloads that need true scale-to-zero with no idle costs.
Question 2: An application requires that user sessions persist even when requests are routed to different EC2 instances. Which solution maintains high availability without sticky sessions?
- Enable ALB sticky sessions with duration-based cookies
- Store session data in Amazon ElastiCache Redis (Correct answer)
- Use NLB instead of ALB for session persistence
- Deploy instances in a single AZ to simplify routing
Correct answer: Store session data in Amazon ElastiCache Redis
Storing sessions in ElastiCache Redis externalizes state so any instance can serve any request, enabling true stateless scaling.
Question 3: A company deploys a Multi-AZ RDS instance and a read replica in a different region. A full region outage occurs. What manual action is required?
- RDS automatically fails over to the cross-region read replica
- The read replica must be manually promoted to a standalone DB instance (Correct answer)
- Route 53 automatically updates to point to the read replica
- The Multi-AZ standby takes over cross-region traffic automatically
Correct answer: The read replica must be manually promoted to a standalone DB instance
Cross-region read replicas require manual promotion during a region outage; they are not part of the automatic Multi-AZ failover mechanism.
Question 4: Which Auto Scaling lifecycle hook allows a custom script to run before an instance is terminated during a scale-in event?
- EC2_INSTANCE_LAUNCHING hook with ABANDON action
- EC2_INSTANCE_TERMINATING hook with CONTINUE action (Correct answer)
- EC2_INSTANCE_TERMINATING hook with ABANDON action
- EC2_INSTANCE_LAUNCHING hook with CONTINUE action
Correct answer: EC2_INSTANCE_TERMINATING hook with CONTINUE action
The EC2_INSTANCE_TERMINATING hook pauses termination, allowing cleanup scripts to run, and CONTINUE resumes the termination afterward.
Question 5: A solutions architect needs an active-active multi-region architecture for a DynamoDB-backed application. Which DynamoDB feature enables this?
- DynamoDB Streams
- DynamoDB Accelerator (DAX)
- DynamoDB Global Tables (Correct answer)
- DynamoDB On-Demand capacity mode
Correct answer: DynamoDB Global Tables
DynamoDB Global Tables provide multi-region, fully replicated tables that support active-active reads and writes in any configured region.
Question 6: An API Gateway REST API experiences throttling errors during peak load. Which strategy reduces throttling without changing the backend architecture?
- Enable API Gateway caching with a TTL (Correct answer)
- Switch to HTTP API from REST API
- Increase the Lambda concurrency limit only
- Disable CloudWatch logging for the API
Correct answer: Enable API Gateway caching with a TTL
API Gateway caching stores responses for a specified TTL, reducing backend calls and throttling during repeated identical requests.
Question 7: A company has an Auto Scaling group behind an ALB. During deployments, they want to avoid sending traffic to instances that are still initializing. Which feature handles this?
- ALB slow start mode
- EC2 Auto Scaling instance warm-up period (Correct answer)
- ALB connection draining (deregistration delay)
- CloudWatch detailed monitoring
Correct answer: EC2 Auto Scaling instance warm-up period
The Auto Scaling instance warm-up period prevents newly launched instances from contributing to scaling metrics until the app is fully initialized.
AWS Certified Solutions Architect High Availability and Scalability 3
A company wants to run a stateless web tier that scales to zero when there is no traffic.
Which AWS service best achieves this with the lowest operational overhead?