Exam SOA-C03 Topic 4 Question 42 Discussion
Actual exam question for Amazon's SOA-C03 exam
Question #: 42
Topic #: 4
Question #: 42
Topic #: 4
A web application runs on Amazon EC2 instances in the us-east-1 Region and the us-west-2 Region. The instances run behind an Application Load Balancer (ALB) in each Region. An Amazon Route 53 hosted zone controls DNS records.
The instances in us-east-1 are production resources. The instances in us-west-2 are for disaster recovery. EC2 Auto Scaling groups are configured based on the ALBRequestCountPerTarget metric in both Regions.
A SysOps administrator must implement a solution that provides failover from us-east-1 to us-west-2. The instances in us-west-2 must be used only for failover.
Which solution will meet these requirements?
The instances in us-east-1 are production resources. The instances in us-west-2 are for disaster recovery. EC2 Auto Scaling groups are configured based on the ALBRequestCountPerTarget metric in both Regions.
A SysOps administrator must implement a solution that provides failover from us-east-1 to us-west-2. The instances in us-west-2 must be used only for failover.
Which solution will meet these requirements?
Suggested Answer: A Vote an answer
Comprehensive and Detailed Explanation From Exact Extract of AWS CloudOps Documents:
The requirement is classic active-passive (production in us-east-1, DR in us-west-2 "only for failover"). The most operationally efficient and purpose-built solution is Route 53 failover routing combined with health checks. With failover routing, Route 53 designates one record as PRIMARY (us-east-1) and another as SECONDARY (us-west-2). Route 53 continuously evaluates the health check associated with the primary endpoint (commonly the ALB DNS name or a specific health-check path). If the primary fails, Route 53 automatically returns the secondary record, directing client DNS resolution to the DR region. This ensures us- west-2 is used only when us-east-1 is unhealthy, directly matching the requirement.
Latency routing (Option B) is designed to route users to the region with the lowest latency, which can actively send traffic to us-west-2 even when us-east-1 is healthy-violating the "DR only" constraint. Options C and D introduce custom automation (CloudWatch + Lambda + DNS record updates) that increases operational overhead, adds failure modes, and is unnecessary because Route 53 already provides managed health-check- based failover. Additionally, "EC2 instance terminated" is not a reliable proxy for full application availability, and DNS modification automation is more complex than using native Route 53 failover policies.
References:
Amazon Route 53 Developer Guide - Health checks and failover routing policy AWS Well-Architected Framework - Reliability pillar (failover, DR patterns) AWS SysOps Administrator Study Guide - DNS failover and Route 53 routing policies
The requirement is classic active-passive (production in us-east-1, DR in us-west-2 "only for failover"). The most operationally efficient and purpose-built solution is Route 53 failover routing combined with health checks. With failover routing, Route 53 designates one record as PRIMARY (us-east-1) and another as SECONDARY (us-west-2). Route 53 continuously evaluates the health check associated with the primary endpoint (commonly the ALB DNS name or a specific health-check path). If the primary fails, Route 53 automatically returns the secondary record, directing client DNS resolution to the DR region. This ensures us- west-2 is used only when us-east-1 is unhealthy, directly matching the requirement.
Latency routing (Option B) is designed to route users to the region with the lowest latency, which can actively send traffic to us-west-2 even when us-east-1 is healthy-violating the "DR only" constraint. Options C and D introduce custom automation (CloudWatch + Lambda + DNS record updates) that increases operational overhead, adds failure modes, and is unnecessary because Route 53 already provides managed health-check- based failover. Additionally, "EC2 instance terminated" is not a reliable proxy for full application availability, and DNS modification automation is more complex than using native Route 53 failover policies.
References:
Amazon Route 53 Developer Guide - Health checks and failover routing policy AWS Well-Architected Framework - Reliability pillar (failover, DR patterns) AWS SysOps Administrator Study Guide - DNS failover and Route 53 routing policies
by Winston at Jan 23, 2026, 09:38 PM
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