AWS DVA-C02 Drill: Blue/Green Deployments in ECS - Rolling Traffic Shifts with CodeDeploy

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 AWS DVA-C02 candidates, the confusion often lies in correctly orchestrating automated ECS deployments that enable gradual traffic shifting without downtime or manual DNS fiddling. In production, this is about knowing exactly how to leverage the AWS::CodeDeploy::BlueGreen hook within CloudFormation to coordinate deployments with ECS and CodeDeploy for safe, incremental user exposure. Let’s drill down.

The Certification Drill (Simulated Question)

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Scenario

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CloudGarage Apps, a fast-growing SaaS company, is modernizing its deployment pipeline. Their lead developer uses AWS CloudFormation templates to automate deployments of containerized applications running on Amazon Elastic Container Service (ECS). The team wants to roll out new application versions gradually—shifting only a percentage of users to the new version initially, and then ramping up to 100% after validation, minimizing risks of broken features. This rollout must be fully automated and orchestrated within CloudFormation pipelines using AWS CodeDeploy.

The Requirement:

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How should the CloudGarage Apps developer configure CloudFormation and CodeDeploy to enable automatic incremental deployments (“blue/green” deployments) that gradually shift user traffic to the new ECS task set before full cutoff?

The Options

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• A) Modify the CloudFormation template to include a Transform section and the AWS::CodeDeploy::BlueGreen hook.
• B) Deploy the new version in a new CloudFormation stack and, after testing, update the application’s DNS records to point to the new stack.
• C) Run CloudFormation stack updates on the existing application stack to deploy new application versions whenever available.
• D) Create a nested CloudFormation stack for the new version including a Transform section and the AWS::CodeDeploy::BlueGreen hook.

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Correct Answer

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A

Quick Insight: The Developer Imperative

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For developer candidates, it’s essential to understand that the AWS::CodeDeploy::BlueGreen hook integrated via CloudFormation Transform (AWS::Include) is the native mechanism to coordinate ECS blue/green deployments with automated traffic shifting. Other methods like manual DNS updates or separate stacks do not provide safe automated percent-based gradual rollouts.

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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Option A is correct because it leverages CloudFormation’s Transform section to enable the AWS::CodeDeploy::BlueGreen hook. This hook is required for ECS to coordinate lifecycle events for blue/green deployments through CodeDeploy. It allows you to automate shifting traffic from the old ECS task set (“blue”) to the new one (“green”) incrementally within the deployment strategy defined in CodeDeploy. This integration ensures a controlled rollout and automatic rollback if health checks fail. The traffic shifting can be done in percentages and automated entirely with CloudFormation and CodeDeploy working in concert.

• The Transform section imports macros necessary for the CodeDeploy blue/green hook.
• This is the AWS recommended best practice for managing blue/green ECS deployments fully within CloudFormation.
• It eliminates manual DNS changes and separate stack deployments that introduce risk and operational overhead.

The Trap (Distractor Analysis)

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• Why not B?
  Deploying in a separate stack and manually changing DNS is error-prone, slow, and lacks automation. It also doesn’t enable incremental traffic shifting, only a hard cutover. This is not suitable for gradual rollouts.

• Why not C?
  Simply running stack updates will deploy new versions but does not orchestrate blue/green deployments with traffic shifting. ECS deployments default to rolling updates or immediate cutovers, lacking safe incremental deployment without CodeDeploy hooks.

• Why not D?
  Nested stacks do not inherently enable the blue/green hook. While nested stacks help modularize templates, the key enabling feature is the inclusion of the Transform section with the CodeDeploy BlueGreen macro in the root template. The added complexity of nested stacks here adds no benefit and may confuse orchestration.

The Technical Blueprint

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# Sample snippet to enable a blue/green ECS deployment with CloudFormation:

Transform: AWS::CodeDeployBlueGreen  # Provided in CloudFormation template

Resources:
  MyEcsService:
    Type: AWS::ECS::Service
    Properties: 
      # ECS service properties, including deployment controller of type CODE_DEPLOY
      DeploymentController:
        Type: CODE_DEPLOY

  MyApplicationDeploymentGroup:
    Type: AWS::CodeDeploy::DeploymentGroup
    Properties:
      DeploymentConfigName: CodeDeployDefault.ECSAllAtOnce
      ServiceRoleArn: !GetAtt CodeDeployServiceRole.Arn
      # Other required CodeDeploy group settings to enable Blue/Green

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 “Include the AWS::CodeDeploy::BlueGreen hook via Transform in CloudFormation” when you see ECS deployments with safe traffic shifting requirements.

Real World

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In reality, many companies use this method to reduce downtime during deployments. An alternative is AWS App Mesh or service mesh solutions for traffic routing, but CodeDeploy’s native blue/green with CloudFormation remains the simplest and most integrated approach without extra infrastructure.

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Disclaimer

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