The answer is to deregister the old instances from the target group with connection draining enabled, then register new instances. This approach works because connection draining, also known as deregistration delay, allows the Network Load Balancer to stop sending new traffic to the old instances while still completing any existing active sessions, thereby preserving sticky session state. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding of how to replace instances without disrupting sticky sessions, a common trap being the impulse to terminate instances immediately or stop the load balancer, both of which would drop active connections. A key memory tip is to think of connection draining as a "graceful goodbye"—it lets the NLB finish serving current clients before removing an instance, ensuring session affinity remains intact during deployments.
SOA-C02 Reliability and Business Continuity Practice Question
This SOA-C02 practice question tests your understanding of reliability and business continuity. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 stateful application on EC2 instances behind a Network Load Balancer (NLB). The application uses sticky sessions (session affinity) to maintain client state. During a deployment, the SysOps administrator needs to replace instances without disrupting active sessions. Which approach should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Deregister the old instances from the target group with connection draining enabled, then register new instances
Correct answer is A. By deregistering instances with a connection draining timeout, the NLB will stop sending new traffic but allow existing connections to complete. Then new instances can be registered. Option B is wrong because terminating instances immediately will drop active sessions. Option C is wrong because stopping the NLB would affect all traffic. Option D is wrong because sticky sessions are not configured on target group health checks; health checks are separate.
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.
✗
Stop the NLB, replace instances, and restart the NLB
Why it's wrong here
Stopping the NLB causes complete outage.
✓
Deregister the old instances from the target group with connection draining enabled, then register new instances
Why this is correct
Connection draining allows existing sessions to finish.
Related concept
Static NAT maps one inside address to one outside address.
✗
Update the target group health check to remove old instances faster
Why it's wrong here
Health checks do not control session draining.
✗
Terminate the old instances immediately and launch new ones
Why it's wrong here
Immediate termination drops active sessions.
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 SOA-C02 NAT questions on configuration and troubleshooting.
Reliability and Business Continuity — This question tests Reliability and Business Continuity — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Deregister the old instances from the target group with connection draining enabled, then register new instances — Correct answer is A. By deregistering instances with a connection draining timeout, the NLB will stop sending new traffic but allow existing connections to complete. Then new instances can be registered. Option B is wrong because terminating instances immediately will drop active sessions. Option C is wrong because stopping the NLB would affect all traffic. Option D is wrong because sticky sessions are not configured on target group health checks; health checks are separate.
What should I do if I get this SOA-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 SOA-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.
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