AWS DVA-C02 Drill: Application Load Balancer - Intelligent Routing for Beta Testing

Jeff’s Note

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Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Lead Developer.

For DVA-C02 candidates, the confusion often lies in how to implement traffic routing to multiple target groups with minimal code changes and infrastructure overhead. In production, this is about knowing exactly how ALB routing rules and cookies can seamlessly direct traffic between app versions without spinning up redundant load balancers or complex Lambda@Edge logic. Let’s drill down.

The Certification Drill (Simulated Question)

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Scenario

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A startup, Pixeloft, operates an image-sharing platform hosted on Amazon EC2 instances managed by an Auto Scaling group. Client requests are balanced by an Application Load Balancer (ALB) whose target group is the current stable version of the web app. Images are stored in a central Amazon S3 bucket. Pixeloft wants to add a new feature that allows their automated testing system to direct requests exclusively to a new beta version of the app without impacting production traffic.

The Requirement:

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Implement this feature with the least development and operational effort possible, enabling test requests to access the beta app version behind the ALB.

The Options

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• A) Create a new Auto Scaling group and target group for the beta app version. Update the ALB’s routing rules to include a condition that inspects a cookie named version with the value beta. Modify the test system to set this cookie in requests to route them to the beta group.

• B) Create an entirely new ALB, Auto Scaling group, and target group for the beta app. Configure an alternate Route 53 DNS record pointing to the new ALB’s endpoint. Use this DNS alias in the test system requests to access the beta version.

• C) Create a new ALB, Auto Scaling group, and target group for the beta version. Use Amazon CloudFront with Lambda@Edge to examine each request and route test requests to the new ALB. Point the test system to the CloudFront distribution URL.

• D) Create a new Auto Scaling group and target group for the beta app. Update the ALB routing rule with a cookie-based condition for version = beta. Use CloudFront with Lambda@Edge to inject the required cookie into test system requests before forwarding them to the ALB.

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Correct Answer

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A

Quick Insight: The Developer Imperative

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Traffic routing by ALB cookie-based rules is a simple, scalable method to split traffic with minimal added infrastructure—no extra ALB or CloudFront layers needed. Modifying the test system code to set a cookie is straightforward and avoids lambda cold starts and complex cache handling inherent in cloudfront + Lambda@Edge. Route 53 DNS-based routing means managing a second ALB and more complexity with no added benefit for selective traffic routing in this case.

Content Locked: The Expert Analysis

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You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?

The Expert’s Analysis

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Correct Answer

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Option A

The Winning Logic

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Using ALB’s native support for routing based on HTTP cookies provides a lightweight, cost-effective method to direct traffic. Creating a separate Auto Scaling group and target group for the beta app is necessary to isolate the beta environment instances. The ALB routing rule evaluates the presence and value of the version cookie and forwards requests accordingly. Updating the test system to set this cookie in requests is a minimal code change that leverages ALB’s built-in routing capability without introducing additional infrastructure.

• This avoids deploying an entirely new ALB or CloudFront distributions, reducing operational overhead.
• No Lambda@Edge coding or cold start issues.
• Cookie-based routing is stable, performant, and easy to maintain.
• Allows granular routing control with simple HTTP features.

The Trap (Distractor Analysis)

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• Why not B?
  Launching a second ALB with a new Auto Scaling group and target group increases cost and complexity. Managing DNS split traffic is less flexible for programmatic routing in testing scenarios.

• Why not C?
  Using CloudFront plus Lambda@Edge to route requests to a separate ALB is overengineering. It adds latency, complexity, and additional cost with little value here. Lambda@Edge should be reserved for advanced request transformation or global content delivery needs.

• Why not D?
  Adding Lambda@Edge just to inject a cookie complicates the architecture unnecessarily. Since the test system can be changed directly to set the cookie, Lambda@Edge is redundant and leads to maintenance overhead.

The Technical Blueprint

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# Example AWS CLI to create ALB rule for cookie-based routing

aws elbv2 create-rule \
  --listener-arn arn:aws:elasticloadbalancing:region:account-id:listener/app/my-alb/xxxxxxx/xxxxxxx \
  --priority 10 \
  --conditions Field=cookie,CookieConfig={CookieName=version,CookieValue=beta} \
  --actions Type=forward,TargetGroupArn=arn:aws:elasticloadbalancing:region:account-id:targetgroup/beta-target-group/xxxxxxxx

The Comparative Analysis

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Real-World Application (Practitioner Insight)

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Exam Rule

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“For the exam, always pick ALB cookie-based routing when you see a need to route only certain user or test requests to different app versions with minimal effort.”

Real World

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“In a real deployment, you might add gradual traffic shifting with weighted target groups or App Mesh for advanced scenarios, but for straightforward A/B or beta testing, cookie-based routing on ALB is the cleanest approach.”

(CTA) Stop Guessing, Start Mastering

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Disclaimer

This is a study note based on simulated scenarios for the AWS DVA-C02 exam.