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 how to implement gradual traffic shifting between Lambda versions without adding unnecessary infrastructure or complexity. In production, this is about knowing exactly how AWS Lambda aliases handle weighted routing natively, and which API resources support this capability. Let’s drill down.
The Certification Drill (Simulated Question) #
Scenario #
TechNova Solutions is preparing to release an update to their core AWS Lambda function that processes customer orders. They want to test the new function version in production by routing half the traffic to the current stable version and half to the newly published version without creating additional Lambda functions or complex routing layers.
The Requirement: #
Enable 50% of the invocation traffic to go to the new Lambda function version and 50% to the current version in the most operationally efficient way.
The Options #
- A) Create two Route 53 records using simple routing policies pointing each to the different Lambda versions. Then create a weighted Route 53 record that routes 50% traffic to each simple record. Use the weighted record to test the Lambda versions.
- B) Create an API Gateway REST API with a POST method integrated with the Lambda function. Add stage variables specifying Lambda function versions. Use a canary deployment that overrides the version variable 50% of the time to test traffic split through API Gateway.
- C) Create a Lambda alias. Configure the alias to route 50% of traffic to the current version and 50% to the new version. Configure the event source mappings to point to this alias for invocation.
- D) Update the event source mapping to assign 50% weight to the current version and 50% to the new version, ensuring the Lambda event source invokes both versions accordingly.
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Correct Answer #
C
Quick Insight: The Developer Imperative #
- AWS Lambda aliases natively support weighted routing between versions, providing built-in traffic shifting without additional networking components.
- Managing this with Route 53 or API Gateway adds unnecessary operational overhead and cost.
- Event source mappings do not support weighted routing across versions, making D incorrect.
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 #
Option C
The Winning Logic #
AWS Lambda supports aliases that can point to multiple function versions with assigned weights, enabling native traffic shifting with minimal configuration. The alias acts as a stable invocation endpoint, routing a specified percentage of invocation requests to each version transparently.
- This approach requires no additional infrastructure (no API Gateway, Route 53 configs).
- Updating event source mappings (like DynamoDB streams or Kinesis) to weighted versions is not supported, so the routing must be handled via aliases.
- It provides seamless, operationally efficient traffic shifting for blue-green deployments or canary tests.
The Trap (Distractor Analysis): #
-
Why not A?
Using Route 53 to direct Lambda traffic is unnecessary and infeasible; Route 53 primarily manages DNS routing and cannot directly integrate with Lambda versions or traffic weights. It adds external complexity outside Lambda’s native capabilities. -
Why not B?
API Gateway stage variables and canary deployment can simulate traffic shifting but require managing another layer (API Gateway) and do not inherently provide version-level weighted routing within Lambda itself. This also increases development and operational overhead. -
Why not D?
Event source mappings lack support for weighted routing to multiple Lambda versions; routing must occur via aliases or version configuration, not via event source mapping weights.
The Technical Blueprint #
# Create an alias with weighted routing of 50% traffic to versions 1 and 2
aws lambda update-alias \
--function-name OrderProcessorFunction \
--name ProdAlias \
--routing-config '{"AdditionalVersionWeights": {"2": 0.5}}' \
--function-version 1
The Comparative Analysis #
| Option | API Complexity | Performance Impact | Use Case |
|---|---|---|---|
| A | High (Complex Route 53 setup) | Indirect, adds latency | Not applicable; DNS can’t route Lambda versions directly |
| B | Moderate (API Gateway config) | Possible cold starts, added latency | Useful for API-level versioning, not Lambda traffic shifting |
| C | Low (Lambda alias weighted routing) | Native, minimal latency | Best for gradual rollout and canary testing within Lambda |
| D | Invalid - event source mappings do not support weights | N/A | Incorrect approach, no native support for weighted invocation |
Real-World Application (Practitioner Insight) #
Exam Rule #
For the exam, always pick Lambda aliases when you see weighted traffic shifting between Lambda versions.
Real World #
In production, we might combine alias weighted routing with monitoring tools like AWS X-Ray or CloudWatch alarms to observe the effects of routing shifts before full rollout.
(CTA) Stop Guessing, Start Mastering #
Disclaimer
This is a study note based on simulated scenarios for the AWS DVA-C02 exam.