SAP-C02 NLB target group stickiness Practice Question
A company runs a stateful application on EC2 instances in an Auto Scaling group behind a Network Load Balancer (NLB). The application requires that client sessions are maintained to the same instance. The operations team notices that after scaling events, some clients lose their sessions. Which configuration change should the team implement to ensure session persistence?
⚠ Common exam trap
Candidates often mistakenly believe that NLB cannot do stickiness or that they must switch to ALB for session persistence. However, NLB supports source IP-based stickiness, which is sufficient for this use case.
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
✓
Enable source IP stickiness on the NLB target group.
Network Load Balancer (NLB) supports target group stickiness based on source IP address, which ensures that client requests are routed to the same EC2 instance, maintaining session persistence. This is the appropriate method for stateful applications. Option A is incorrect because disabling cross-zone load balancing does not provide stickiness; it only restricts traffic to instances in the same Availability Zone. Option B is incorrect because NLB does not support cookie-based stickiness; that is a feature of Application Load Balancer. Option C is incorrect because while ALB does support cookie-based stickiness, switching to ALB is unnecessary; NLB already supports source IP stickiness.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Disable cross-zone load balancing on the NLB.
Why it's wrong here
Disabling cross-zone load balancing does not ensure session persistence; it only limits traffic distribution to instances within the same Availability Zone.
- ✗
Enable cookie-based stickiness on the NLB listener.
Why it's wrong here
NLB does not support cookie-based stickiness; that feature is only available on Application Load Balancer.
- ✗
Switch to an Application Load Balancer and enable cookie-based stickiness.
Why it's wrong here
Switching to ALB is unnecessary because NLB already provides source IP-based stickiness, which meets the requirement.
- ✓
Enable source IP stickiness on the NLB target group.
Why this is correct
NLB target groups can be configured with source IP stickiness, which binds a client's session to a specific target instance based on the client's IP address.
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