DOP-C02 Incident and Event Response Practice Question
A company runs a critical web application on AWS. The application is deployed on EC2 instances behind an Application Load Balancer (ALB). The instances are in an Auto Scaling group across multiple Availability Zones. The company uses Amazon Route 53 for DNS with a failover routing policy. Recently, the operations team noticed that during a regional outage, the failover did not trigger as expected, and users experienced downtime. The health checks in Route 53 are configured to check the ALB endpoint. The ALB's health checks are configured to check the instances. What is the MOST likely reason the failover did not work?
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
✓
The ALB remained healthy during the regional outage, so Route 53 did not fail over.
Route 53 health checks are configured to check the ALB endpoint. During a regional outage, if the ALB itself remains healthy (e.g., the outage only affected the instances but not the ALB), the health check passes, so Route 53 does not trigger failover. This leads to users experiencing downtime because the instances behind the ALB are unhealthy, but Route 53 still directs traffic to the primary region. Option B is incorrect because failover with Route 53 is automatic when a health check fails; no manual intervention is required. Option C is incorrect because Route 53 health checks do not need to check instance IPs; checking the ALB is sufficient for failover as long as the ALB's health reflects instance health, but in this case it doesn't. Option D is incorrect because Route 53 can failover to a different region when the primary endpoint becomes unhealthy, but the condition for failover (health check failure) was not met.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The ALB remained healthy during the regional outage, so Route 53 did not fail over.
Why this is correct
The health check associated with the primary ALB endpoint continued to receive a valid HTTP 200 response, so Route 53 considered the resource healthy and did not trigger failover to the secondary region. Even though an AZ was experiencing an outage, the ALB is a regional service that can remain available if it is deployed in other AZs, or the outage may have been in a different part of the region. Since the health check threshold was never breached, Route 53 had no reason to update DNS records.
- ✗
The failover routing policy requires manual intervention to switch traffic.
Why it's wrong here
Failover routing policy in Route 53 is fully automated; when a health check fails, Route 53 automatically switches the DNS response from the primary to the secondary resource. No manual intervention is required, and an administrator does not need to change any records or wait for a human to flip a switch. The correct reason for no failover is that the health check never reported the primary as unhealthy.
- ✗
Route 53 health checks were not configured for the instance IP addresses.
Why it's wrong here
Route 53 health checks for an Application Load Balancer are typically configured against the ALB's DNS name or IP address, not the individual EC2 instance IPs. The instances themselves do not need to be directly registered with Route 53; the ALB health checks the instances separately and only Route 53's health check of the ALB endpoint determines failover. Thus, absence of instance-IP health checks is irrelevant.
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Route 53 cannot failover to a different region when the primary endpoint is still reachable.
Why it's wrong here
Route 53 can absolutely fail over to a different region even when the primary endpoint is still technically reachable; the decision is based on the status of the configured health check, not a generic reachability ping. For example, if the health check is configured with a specific path or expects a particular status code that returns an error, failover would occur despite the endpoint responding at a network level. In this scenario, however, the health check for the ALB remained healthy, so the condition for failover was not met.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DOP-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DOP-C02 exam.