The answer is an Auto Scaling group, because it is the AWS service designed to automatically terminate and replace EC2 instances that fail health checks, including those from an Application Load Balancer. This works by integrating the load balancer’s health check status with the Auto Scaling group’s health check configuration, so when an instance is marked unhealthy, the group launches a new instance to maintain the desired capacity. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this concept tests your understanding of how Auto Scaling groups handle fault tolerance and high availability at the network layer, often appearing in scenarios where you must distinguish between monitoring (CloudWatch) and automated remediation. A common trap is choosing Lambda for custom logic, but the standard, managed solution is always the Auto Scaling group. Memory tip: think “Auto Scaling = Auto Replacement” — the group’s core job is to keep your fleet healthy by swapping out bad instances.
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. 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 company runs a critical application on EC2 instances behind an Application Load Balancer. They need to ensure that if an instance fails health checks, it is automatically terminated and replaced. Which AWS service should they use?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Auto Scaling group
The correct answer is D because Auto Scaling groups can automatically replace unhealthy instances based on health checks from the load balancer. Option A (EC2) does not provide automatic replacement. Option B (CloudWatch) can monitor but not replace. Option C (Lambda) could be used with custom logic but is not the standard solution.
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.
✗
AWS Lambda
Why it's wrong here
Lambda could be used with custom automation, but it is not the native service for this purpose.
✗
EC2 Instance Connect
Why it's wrong here
EC2 Instance Connect allows SSH access but does not manage instance health or replacement.
✓
Auto Scaling group
Why this is correct
Auto Scaling groups can use ELB health checks to automatically replace unhealthy instances.
Related concept
Static NAT maps one inside address to one outside address.
✗
Amazon CloudWatch
Why it's wrong here
CloudWatch can monitor and alarm but cannot automatically terminate and replace instances.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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 ANS-C01 NAT questions on configuration and troubleshooting.
Network Implementation — This question tests Network Implementation — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Auto Scaling group — The correct answer is D because Auto Scaling groups can automatically replace unhealthy instances based on health checks from the load balancer. Option A (EC2) does not provide automatic replacement. Option B (CloudWatch) can monitor but not replace. Option C (Lambda) could be used with custom logic but is not the standard solution.
What should I do if I get this ANS-C01 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 ANS-C01 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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