Use case

When using provisioned concurrency or other non-on-demand invocation types in Lambda functions, the first invocation is not necessarily a cold start. For instance, SnapStart doesn't have cold starts at all (only restores).

Currently, Powertools incorrectly identifies these scenarios as cold starts, leading to:

• Cold start metrics being emitted when they shouldn't be
• JSON logs showing cold_start: true field incorrectly
• Traces having ColdStart: true annotation when inappropriate

This creates inaccurate observability data for Lambda functions using provisioned concurrency or SnapStart.

Solution/User Experience

All function executions which do not have AWS_LAMBDA_INITIALIZATION_TYPE="on-demand" should:

• NOT emit a cold start metric
• NOT set cold_start: true in the structured JSON logs
• NOT set the ColdStart annotation in traces

Implementation approach:
Use the AWS_LAMBDA_INITIALIZATION_TYPE environment variable within the utilities to suppress cold start behavior if the init type is not on-demand. Consider all init types from the AWS docs: https://docs.aws.amazon.com/lambda/latest/dg/configuration-envvars.html#configuration-envvars-runtime

Update the global LambdaHandlerProcessor to have more nuanced cold start detection logic:

Code example:

@Logging(logEvent = true)
@Tracing
@FlushMetrics(namespace = "TriagingTemplate", service = "triage", captureColdStart = true)
public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent input, Context context) {
    // With provisioned concurrency, this should NOT be marked as cold start
    logger.info("Processing triage request");
    metrics.addMetric("TriageRequests", 1, MetricUnit.COUNT);
    // ... rest of handler
}

Reproduction steps:
Deploy a Lambda function with provisioned concurrency using this SAM template. You can use the Powertools triaging template for this: https://github.com/phipag/powertools-triaging-template-java

TriageFunction:
  Type: AWS::Serverless::Function
  Properties:
    CodeUri: .
    Handler: triage.TriageHandler::handleRequest
    AutoPublishAlias: live
    ProvisionedConcurrencyConfig:
      ProvisionedConcurrentExecutions: 1

Alternative solutions

Using AWS_LAMBDA_INITIALIZATION_TYPE is the most reliable and AWS-native approach.

Acknowledgment

• This feature request meets Powertools for AWS Lambda (Java) Tenets
• Should this be considered in other Powertools for AWS Lambda languages? i.e. Python, TypeScript, and .NET

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