The correct response to an EC2 status check failure in Auto Scaling is to first verify the instance’s system and instance status checks, then consider terminating the instance so the Auto Scaling group can launch a replacement. This is because EC2 status checks are internal health probes that detect issues like operating system failures, network misconfigurations, or hardware degradation—problems that cannot be resolved by adjusting security groups or waiting for automatic recovery. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of how Auto Scaling integrates with EC2 health checks and the lifecycle of instances within a group. A common trap is assuming the Auto Scaling group will automatically replace a failed instance without termination; in reality, it only launches a new instance if the existing one is terminated or explicitly marked unhealthy via a health check grace period. Memory tip: “Check, then chuck”—verify the health check details first, then terminate to trigger replacement.
DOP-C02 Incident and Event Response Practice Question
This DOP-C02 practice question tests your understanding of incident and event response. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A DevOps engineer receives an alarm that an EC2 instance's status check has failed. The instance is part of an Auto Scaling group. How should the engineer respond?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Verify the instance's system and instance status checks, then consider terminating the instance to allow the Auto Scaling group to launch a new one
Option B is correct because if the instance fails status checks, the engineer should verify the instance is healthy and replace it if needed. Option A is wrong because status checks are internal, not security group issues; C is wrong because terminating the instance manually may not be necessary; D is wrong because the Auto Scaling group will launch a new instance only if the instance is terminated or marked unhealthy.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Immediately terminate the instance to trigger a replacement
Why it's wrong here
Terminating without verification may cause unnecessary disruption.
✓
Verify the instance's system and instance status checks, then consider terminating the instance to allow the Auto Scaling group to launch a new one
Why this is correct
This is the correct response to a status check failure.
Related concept
Static NAT maps one inside address to one outside address.
✗
Do nothing, because the Auto Scaling group will automatically replace the instance
Why it's wrong here
Auto Scaling replaces only if the instance is terminated or marked unhealthy.
✗
Check the security group rules to ensure they allow traffic
Why it's wrong here
Status checks are not affected by security groups.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DOP-C02 NAT questions on configuration and troubleshooting.
Incident and Event Response — This question tests Incident and Event Response — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Verify the instance's system and instance status checks, then consider terminating the instance to allow the Auto Scaling group to launch a new one — Option B is correct because if the instance fails status checks, the engineer should verify the instance is healthy and replace it if needed. Option A is wrong because status checks are internal, not security group issues; C is wrong because terminating the instance manually may not be necessary; D is wrong because the Auto Scaling group will launch a new instance only if the instance is terminated or marked unhealthy.
What should I do if I get this DOP-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DOP-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A DevOps engineer receives a CloudWatch alarm that the 'StatusCheckFailed' metric for an EC2 instance is in ALARM state. The instance is part of an Auto Scaling group. What should the engineer do first to restore service?
easy
A.Update the Auto Scaling group's launch configuration
✓ B.Wait for Auto Scaling to replace the instance
C.Manually terminate the instance
D.Reboot the instance
Why B: Option B is correct because the instance status check failure indicates a system issue; if the instance is unhealthy, Auto Scaling will terminate and replace it. Option A is wrong because rebooting may not fix underlying issues. Option C is wrong because terminating manually is not needed; Auto Scaling handles it. Option D is wrong because changing the AMI is not immediate.
Last reviewed: Jun 20, 2026
Question Discussion
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