SAA-C03 Design High-Performing Architectures Practice Question
You run a web application on an EC2 Auto Scaling group behind an Application Load Balancer (ALB). During scheduled traffic spikes, new instances launch but customers occasionally see 5xx errors for the first few minutes after scale-out. Operational logs show instances need ~4 minutes to warm up (load caches and initialize dependencies). ALB target health becomes healthy only after this warm-up. Which change most directly improves performance during spikes by reducing the time to serve traffic after scaling?
⚠ Common exam trap
Candidates often think NLB bypasses health checks entirely, but in reality NLB still requires health checks to mark targets as healthy, and the application warm-up delay remains the bottleneck.
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
✓
Use an Auto Scaling warm pool so instances are pre-initialized and ready to register quickly when the ASG scales out.
B is correct because a warm pool pre-initializes instances (e.g., loading caches and dependencies) before they are added to the Auto Scaling group. When the ASG scales out, these pre-warmed instances can be quickly moved into service, bypassing the ~4-minute warm-up delay and reducing the window for 5xx errors.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure a larger ALB deregistration delay so that old targets remain longer before termination.
Why it's wrong here
ALB deregistration delay affects how long existing targets are kept during scale-in events and connection draining behavior. It does not reduce the initialization/warm-up time of newly launched instances. If new instances cannot become healthy until warm-up completes, customers can still see 5xx responses during the initial minutes after scale-out.
- ✓
Use an Auto Scaling warm pool so instances are pre-initialized and ready to register quickly when the ASG scales out.
Why this is correct
With a warm pool, Auto Scaling can launch and keep a set of instances in a pre-initialized state (for example, instances are already booted and have completed parts of startup/initialization as supported by warm pool behavior). When scaling triggers, these instances can transition to service faster and begin registering with the ALB. Because your bottleneck is that instances take ~4 minutes to become truly ready, warming them ahead of time most directly reduces the gap between scale-out and customer-ready capacity (and therefore reduces 5xx occurrences while waiting for targets to pass ALB health checks).
- ✗
Increase the number of desired instances immediately without using scaling policies, and then rely on manual reconfiguration.
Why it's wrong here
Manually changing desired capacity can work in an operational sense, but it is not a direct improvement to application warm-up time, and it is not responsive/automated for demand variability. It also doesn’t solve the core issue: newly created instances still require the same warm-up duration before they pass ALB health checks.
- ✗
Switch from ALB to NLB so instances become reachable sooner without waiting for health checks.
Why it's wrong here
NLB does not inherently remove the application’s initialization requirement. While health check behavior differs by load balancer type (e.g., NLB often uses TCP-level checks), the application still needs time to become ready to handle requests successfully. Switching to NLB may change routing and health-check characteristics, but it does not directly address the ~4-minute warm-up bottleneck.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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