On the exam, you’ll often see questions about how to gracefully handle in-flight requests when Auto Scaling scales in. The common trap is confusing cooldown periods with deregistration delay. Cooldowns affect scaling behavior, but deregistration delay ensures requests already in progress finish before termination.
Let’s walk through a fresh scenario, break down why deregistration delay is the right answer, and summarize with cheat sheets, exam tips, and highlights.
Scenario
A financial analytics platform runs on Amazon EC2 instances behind an Application Load Balancer (ALB). The EC2 instances are part of an Auto Scaling group.
During month-end close, users generate large data exports that may take up to 10 minutes.
The operations team is concerned that if Auto Scaling scales in, active exports will fail and customers will see errors.
The company wants to make sure all running requests are completed before instances are shut down.
Solution – Increase the Deregistration Delay Timeout
The team configures the deregistration delay for the ALB target group to be greater than 600 seconds.
By default, the ALB waits 300 seconds (5 minutes) before deregistering an instance.
Extending the delay ensures that long-running requests finish before the instance is fully removed.
The instance will not receive new connections but remains active to finish any in-flight work.
This prevents users from losing progress during long-running exports.
Cheat Sheet: Cooldown vs Deregistration Delay
Setting | Purpose | Exam Clue |
|---|---|---|
Deregistration Delay | Lets in-flight requests complete before termination | Clue: “Ensure requests finish before shutdown” |
Cooldown Period | Prevents Auto Scaling from making rapid changes | Clue: “Stabilize scaling decisions” |
Cheat Sheet: ALB Scale-In Behavior
Feature | Default | Configurable To | Use Case |
|---|---|---|---|
Deregistration Delay | 300 seconds | Up to 3,600 seconds | Graceful handling of long requests |
Connection Draining | Enabled automatically | Adjustable via target group | Ensures no new requests hit deregistering instances |
Exam Tips
Exam Tip | Key Point | Why It Matters |
|---|---|---|
Deregistration Delay = Protects Active Requests | Allows graceful completion | Correct for reports, exports, uploads |
Cooldown ≠ Request Handling | Only controls scaling behavior | Common distractor |
Default = 300s | Increase if workloads >5 min | Expect exam numbers in scenario |
Configured on Target Group | Keywords: “target group deregistration delay” | Exam clue for ALB-related questions |
Exam Highlights
This maps to Domain 2: Design Resilient Architectures.
Deregistration delay = ensures customer requests aren’t interrupted during scale-in.
Cooldown = governs Auto Scaling timing, not request handling.
Exam keywords: “long-running requests,” “scale-in,” “prevent errors,” “graceful shutdown.”
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