DVA-C02 Deployment Practice Question
A developer wants to deploy a serverless application using AWS CloudFormation. The application consists of an API Gateway, Lambda functions, and DynamoDB tables. The developer wants to ensure that the stack can be updated without resource interruption when possible. Which CloudFormation feature should the developer use?
⚠ Common exam trap
Watch out — candidates often confuse ChangeSets (which only preview changes) with the actual update mechanism, or they mistakenly think StackPolicies or Custom Resources can control update behavior, when in fact only the `DeploymentPreference` update policy on a Lambda alias provides the traffic-shifting capability needed for uninterrupted updates.
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 a Lambda alias with a DeploymentPreference update policy
The `DeploymentPreference` update policy on a Lambda alias enables canary, linear, or all-at-once traffic shifting during stack updates. This allows the developer to update Lambda function versions without interrupting existing invocations, as traffic is gradually routed to the new version while the old version continues to serve requests until the transition completes.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Use a Lambda alias with a DeploymentPreference update policy
Why this is correct
CloudFormation's `AWS::Lambda::Alias` resource, when combined with a `DeploymentPreference` update policy, facilitates controlled, gradual traffic shifting between a Lambda function's current version and a newly deployed version. This strategy leverages AWS CodeDeploy to manage the rollout, allowing for canary deployments or linear shifts, which ensures that updates are applied without service interruption by routing traffic incrementally and automatically rolling back if issues are detected.
- ✗
Use a ChangeSet to review changes before applying them
Why it's wrong here
A CloudFormation Change Set provides a preview of the proposed modifications to your stack resources before they are actually implemented. While invaluable for understanding the impact of an update, it is purely a planning tool. Executing a Change Set still involves CloudFormation directly modifying resources, and if those modifications require recreating or temporarily disabling a resource, the Change Set itself offers no mechanism to prevent service interruption during that process.
- ✗
Use a StackPolicy to protect critical resources
Why it's wrong here
A CloudFormation Stack Policy is designed to prevent unintended updates or deletions of specific resources within a stack, acting as a safeguard against accidental modifications to critical components. However, its purpose is protection, not graceful deployment. For resources *not* protected by the policy, or for updates that are explicitly allowed, the Stack Policy does not provide any mechanism to ensure zero-downtime updates or prevent service interruption during their modification.
- ✗
Use a Custom Resource to manage updates
Why it's wrong here
CloudFormation Custom Resources allow you to write custom provisioning logic, typically using a Lambda function, to manage resources not natively supported by CloudFormation or to perform complex operations. While powerful for extending CloudFormation's capabilities, a Custom Resource merely executes custom code during stack operations. It does not inherently provide traffic shifting, blue/green deployment, or any other built-in mechanism to prevent service interruption for other resources being updated by the CloudFormation stack itself.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DVA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DVA-C02 exam.