The AWS Lambda Extensions API seems to set the tracing field in the INVOKE event for Lambda extensions even if X-Ray active tracing is disabled for the Lambda function and the requesting service (e.g., API Gateway) doesn't provide tracing headers. It's unclear where the trace ID originates, but I confirmed that it's present even when X-Ray is disabled. When I searched the trace ID in the X-Ray console, it didn't find anything, suggesting that the AWS Lambda service generates a new trace ID when none is provided.
When locally testing Lambda extensions using the Rust runtime and the AWS SAM CLI's sam local command, extensions fail with a "missing field tracing" error. The same extensions work fine in production.
Since this incompatibility is due to a behavioral difference between the AWS Lambda service in production and the emulator, I think it's ultimately a bug in the emulator, rather than the Rust runtime being overly strict.
I'd suggest changing the NewXRayTracing function to generate a trace ID when none is provided, rather than returning nil.
The AWS Lambda Extensions API seems to set the
tracingfield in theINVOKEevent for Lambda extensions even if X-Ray active tracing is disabled for the Lambda function and the requesting service (e.g., API Gateway) doesn't provide tracing headers. It's unclear where the trace ID originates, but I confirmed that it's present even when X-Ray is disabled. When I searched the trace ID in the X-Ray console, it didn't find anything, suggesting that the AWS Lambda service generates a new trace ID when none is provided.However, the emulator omits this field when the request doesn't include an
X-Amzn-Trace-Idheader: https://github.com/aws/aws-lambda-runtime-interface-emulator/blob/2057adac54dbd781b51431f775363ec021648c77/lambda/rapi/rendering/rendering.go#L144 https://github.com/aws/aws-lambda-runtime-interface-emulator/blob/2057adac54dbd781b51431f775363ec021648c77/lambda/rapi/model/tracing.go#L30-L33This behavior breaks compatibility with the AWS Lambda Rust Runtime, which expects the
tracingfield (cc @calavera): https://github.com/awslabs/aws-lambda-rust-runtime/blob/ab3b809d63fad05369596d17ad4fc449f7035e5e/lambda-extension/src/events.rs#L23When locally testing Lambda extensions using the Rust runtime and the AWS SAM CLI's
sam localcommand, extensions fail with a "missing fieldtracing" error. The same extensions work fine in production.Since this incompatibility is due to a behavioral difference between the AWS Lambda service in production and the emulator, I think it's ultimately a bug in the emulator, rather than the Rust runtime being overly strict.
I'd suggest changing the
NewXRayTracingfunction to generate a trace ID when none is provided, rather than returningnil.