Jeff’s Note #
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 understanding how Lambda versioning combined with aliases enables controlled traffic shifting without downtime. In production, this is about knowing exactly how to deploy new Lambda versions safely and route partial user traffic for canary-style testing. Let’s drill down.
The Certification Drill (Simulated Question) #
Scenario #
Imagine you are a lead developer at PixelCraft, a startup specializing in photo editing apps. Your application uses an AWS Lambda function to process user-uploaded photos with various filters and enhancements. A new feature requires you to update this Lambda function’s code. However, you must ensure the update is tested in production by gradually shifting user requests from the current version of the Lambda function to the new version without impacting all users at once.
The Requirement: #
You need to update the Lambda function and test the changes by splitting live user traffic between the stable version and the updated version of the Lambda function.
The Options #
- A) Publish a version of the original Lambda function. Make the necessary changes to the Lambda code. Publish a new version of the Lambda function.
- B) Use AWS CodeBuild to detect updates to the Lambda function. Configure CodeBuild to incrementally shift traffic from the original version of the Lambda function to the new version of the Lambda function.
- C) Update the original version of the Lambda function to add a function URL. Make the necessary changes to the Lambda code. Publish another function URL for the updated Lambda code.
- D) Create an alias that points to the original version of the Lambda function. Configure the alias to be a weighted alias that also includes the new version of the Lambda function. Divide traffic between the two versions.
- E) Create an alias that points to the original function URL. Configure the alias to be a weighted alias that also includes the additional function URL. Divide traffic between the two function URLs.
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Correct Answer #
A and D
Quick Insight: The Lambda Traffic Shifting Imperative #
- For Developers: Understanding Lambda function versioning and the use of weighted aliases is critical. Versions give you immutable snapshots of your code. Aliases enable traffic routing, allowing precise control of what percentage of requests go to which version.
- Why Not Others: There is no direct support for traffic shifting using function URLs or CodeBuild alone, and function URLs cannot be aliased or weighted.
Content Locked: The Expert Analysis #
You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?
The Expert’s Analysis #
Correct Answer #
Options A and D
The Winning Logic #
- Option A is critical because you first need to publish immutable versions of the Lambda function before you can do any traffic shifting. The version encapsulates a snapshot of your function code and configuration.
- Option D implements the canary deployment by creating a Lambda alias and configuring weighted traffic routing between different versions. This leverages the built-in Lambda feature for controlled deployment and testing of new code.
Using weighted aliases allows you to gradually shift a percentage of live traffic to the new function version without downtime or disruption to all users.
The Trap (Distractor Analysis): #
- Why not B? CodeBuild is a build and test orchestration service; it does not natively manage Lambda traffic shifting. It cannot progressively route user requests between different Lambda versions.
- Why not C? Function URLs are HTTP endpoints and don’t support versioning or traffic weighting. You cannot create aliases for function URLs or split traffic between URLs in the same fine-grained way.
- Why not E? Aliases do not point to function URLs, and weighted aliases cannot be applied to URLs—only to Lambda function versions. This option violates AWS Lambda versioning and alias rules.
The Technical Blueprint #
# Publish a new version after code update (part of Option A)
aws lambda publish-version --function-name PhotoEditorFunction
# Create or update an alias for traffic shifting (part of Option D)
aws lambda create-alias \
--function-name PhotoEditorFunction \
--name ProdAlias \
--function-version 1
aws lambda update-alias \
--function-name PhotoEditorFunction \
--name ProdAlias \
--routing-config '{"AdditionalVersionWeights": {"2": 0.2}}'
The Comparative Analysis #
| Option | API Complexity | Performance Impact | Use Case |
|---|---|---|---|
| A | Moderate (versioning) | None | Required to snapshot Lambda function code |
| B | High (CI/CD setup) | None | Incorrect for traffic shifting |
| C | Low | None | Incorrect: function URLs cannot be weighted |
| D | Moderate | Minimal overhead | Correct approach for weighted traffic routing |
| E | Moderate | None | Invalid: aliases can’t route to URLs |
Real-World Application (Practitioner Insight) #
Exam Rule #
For the exam, always pick Lambda versions with weighted aliases when you want to split production traffic between function versions.
Real World #
In reality, teams also combine this with CI/CD pipelines and monitoring (like AWS X-Ray) to observe the impact of incremental traffic shifts before full cutover.
(CTA) Stop Guessing, Start Mastering #
Disclaimer
This is a study note based on simulated scenarios for the AWS DVA-C02 exam.