AWS DVA-C02 Drill: Lambda Deployment Rollback - Minimizing User Impact

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 use Lambda versioning and aliases effectively to roll back deployments without impacting users. In production, this is about knowing exactly how weighted aliases enable traffic shifting and rollbacks with minimal downtime and risk. Let’s drill down.

The Certification Drill (Simulated Question)

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Scenario

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TechVantage Solutions is an agile startup building a customer-facing API using AWS Lambda. To ensure continuous delivery, they release new Lambda function versions frequently. However, when a newly deployed version introduces errors, they need a way to quickly roll back to the previous stable version without affecting user experience or requiring changes to the client applications.

The Requirement:

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Design a Lambda deployment strategy that allows seamless rollback to a previous function version with minimal impact on application users.

The Options

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• A) Change the client application to invoke a Lambda alias that points to the current stable version. Deploy the new Lambda version. Update the alias to point to the new version. If errors occur, update the alias back to the previous version.
• B) Change the client application to invoke a Lambda alias that points to the current stable version. Deploy the new Lambda version. Update the alias to route 10% of traffic to the new version. If too many errors are detected, route 100% of traffic back to the previous version.
• C) Do not change the client application. Deploy the new Lambda version. If errors occur, modify the client to invoke the Lambda function by the previous version’s Amazon Resource Name (ARN).
• D) Create three Lambda aliases: “new”, “existing”, and “router”. Point “existing” to the stable version and “new” to the new version. Have the client invoke the “router” alias, which initially directs 100% of traffic to “existing”. After deployment, update “router” to send 10% traffic to “new”. If problems arise, route 100% back to “existing”.

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Correct Answer

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B

Quick Insight: The Developer Imperative

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Lambda aliases support weighted traffic shifting between published versions. Using weighted aliases lets you do a canary deployment by sending a small percentage of requests to the new version. If this test reveals issues, you quickly roll back all traffic with just an alias update—no client changes needed. This approach minimizes user impact and supports iterative delivery.

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 B

The Winning Logic

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Option B leverages Lambda aliases with weighted traffic shifting, which is the recommended best practice for safe deployments and rollbacks. The client invokes a stable alias that initially points 100% to the current version. Upon deploying a new version, the alias is updated to route only 10% of traffic to the new code (a canary release). This controlled rollout exposes only 10% of users to potential errors, minimizing impact. If errors exceed thresholds, the alias is reverted to send 100% of traffic back to the previous version, instantly rolling back without code or client changes.

• Lambda aliases decouple client invocation from specific version ARNs.
• Weighted alias updates avoid cold starts and configuration disruptions.
• No updates required to the client code or deployment of additional aliases.
• Supports gradual rollouts, easy rollback, and safe testing in production.

The Trap (Distractor Analysis):

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• Why not A? Although alias pointing is correct, switching the alias from 100% old to 100% new at once risks all users experiencing errors instead of a gradual rollout. No weighted traffic control.
• Why not C? Requires client changes to invoke specific version ARNs when rolling back, increasing operational complexity and risk.
• Why not D? Overly complex with multiple aliases and an additional “router” alias, which is unnecessary and complicates client invocation, increasing maintenance overhead.

The Technical Blueprint

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Relevant AWS CLI snippet to configure alias weighted routing:

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# Create alias 'prod' pointing to version 1 (current stable)
aws lambda create-alias --function-name MyFunction --name prod --function-version 1

# Deploy new version 2 and update alias to route 10% traffic to version 2
aws lambda update-alias --function-name MyFunction --name prod \
  --routing-config '{"AdditionalVersionWeights":{"2":0.1}}'

# To rollback completely, update alias back to 100% version 1
aws lambda update-alias --function-name MyFunction --name prod --function-version 1

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 Lambda aliases with weighted traffic shifting when you see needs for zero-downtime deployment and rollback.

Real World

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In practice, teams integrate Lambda weighted aliases into CI/CD pipelines (e.g., CodePipeline) to automate progressive deployments. Monitoring tied with alarms can trigger automatic rollback by reverting alias weights—making deployment safer and user impact minimal.

(CTA) Stop Guessing, Start Mastering

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Disclaimer

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