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I have a Flask app running as an AWS Lambda Function deployed with Zappa and would like to activate X-Ray to get more information for the different functions.

Activating X-Ray with Zappa was easy enough - it only requires adding this line in the zappa-settings.json:

"xray_tracing": true

Further, I installed the AWS X-Ray Python SDK and added a few decorators to some functions, like this:

@xray_recorder.capture()

When I deploy this as a Lambda function, it all works well. The problem is using the system locally, both when running tests and when running the Flask in a local server instead of as a lambda function.

When I use any of the functions that are decorated either in a test or through the local server, the following exception is thrown:

aws_xray_sdk.core.exceptions.exceptions.SegmentNotFoundException: cannot find the current segment/subsegment, please make sure you have a segment open

Which of course makes sense, because AWS Lambda handles the creation of segments.

Are there any good ways to deactivate capturing locally? This would be useful e.g. for running unit tests locally on functions that I would like to watch in X-Ray.

Thomas D. Frøysa
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1 Answers1

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One of the feature request of this SDK is to have a "disabled" global flag so everything becomes no-ops https://github.com/aws/aws-xray-sdk-python/issues/26.

However, it still depends on what you are testing against. It's good practice to test what actually will be run on Lambda. You can set some environment variables so the SDK thinks it is running on Lambda.

You can see the SDK is looking for two env vars https://github.com/aws/aws-xray-sdk-python/blob/master/aws_xray_sdk/core/lambda_launcher.py. One is LAMBDA_TASK_ROOT set to true so it knows to switch to lambda-mode. The other one is _X_AMZN_TRACE_ID which contains the tracing context normally passed by lambda container.

If you just want to test non-XRay code you can set AWS_XRAY_CONTEXT_MISSING to LOG_ERROR so the SDK doesn't complain on context missing and simply give up capturing wrapped functions. This will run much less code path than mimic lambda behaviors. Ideally it would be better for the lambda local testing tool to be X-Ray friendly. Are you using https://github.com/awslabs/aws-sam-cli? There is already an open issue for this feature https://github.com/awslabs/aws-sam-cli/issues/217

haotian465
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