AWS Certified Solutions Architect Professional SAP-C02 Practice Question
A company operates its public REST API in two AWS Regions. The primary stack runs behind an Application Load Balancer (ALB) in us-east-1, and an identical standby stack runs behind an ALB in ap-southeast-2. The business continuity plan requires that clients automatically fail over to the standby Region if the primary ALB or its Region becomes unavailable. Additional requirements:
Failover must occur within about 1 minute of an outage.
The DNS solution must avoid single points of failure and require no self-managed infrastructure.
How should a solutions architect configure Amazon Route 53 to meet these requirements in the MOST cost-effective way?
Create a public hosted zone and configure two alias A records with a Failover routing policy. Point the primary record to the us-east-1 ALB and the secondary record to the ap-southeast-2 ALB. For both records, set 'Evaluate Target Health' to true.
Deploy AWS Global Accelerator with both ALBs as endpoints and create a CNAME record that maps the API hostname to the accelerator DNS name.
Create two latency-based alias A records, one for each ALB, and set 'Evaluate Target Health' to true for both. This will allow Route 53 to shift traffic away from an unhealthy Region.
Use weighted routing records, assigning a weight of 100 to the primary ALB and 0 to the standby ALB. Associate a Route 53 health check with each record and set the TTL to 60 seconds.
Route 53 failover routing is designed specifically for active-passive disaster recovery scenarios. Using alias A records that point to Application Load Balancers is a best practice, as it avoids managing the changing IP addresses of the ALBs. When 'Evaluate Target Health' is enabled on an alias record, Route 53 automatically uses the health status of the ALB to determine if the record is healthy. If the primary ALB's target groups become unhealthy or the ALB itself fails, Route 53 will mark the primary alias record as unhealthy and begin responding to DNS queries with the secondary (failover) record.
The TTL for an alias record pointing to an ALB is automatically set to 60 seconds and is not configurable. This inherent low TTL ensures that DNS resolvers quickly stop caching the IP address of the failed primary ALB, allowing client traffic to shift to the standby Region within the required 1-minute RTO.
Latency-based routing is for active-active setups, not active-passive. Weighted routing can simulate failover but is less direct than using the purpose-built Failover routing policy. AWS Global Accelerator meets the technical requirements but is significantly more expensive than a Route 53 DNS failover solution and is therefore not the most cost-effective option.
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AWS Certified Solutions Architect Professional SAP-C02
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