python-tracing.md

Instrumenting Python Code in AWS Lambda

In Python, you can have Lambda emit subsegments to X-Ray to show you information about downstream calls to other AWS services made by your function. To do so, you first need to include the the AWS X-Ray SDK for Python in your deployment package. In addition, you can patch the boto3 (or botocore if you are using sessions), so any client you create to access other AWS services will automatically be traced by X-Ray.

import boto3
from aws_xray_sdk.core import xray_recorder
from aws_xray_sdk.core import patch

patch(['boto3'])

Once you've patched the module you are using to create clients, you can use it to create your traced clients, in the case below Amazon S3:

s3_client = boto3.client('s3')

The X-Ray SDK for Python creates a subsegment for the call and records information from the request and response. You can use the aws_xray_sdk_sdk.core.xray_recorder to create subsegments automatically by decorating your Lambda functions or manually by calling xray_recorder.begin_subsegment() and xray_recorder.end_subsegment() inside the function, as shown in the following Lambda function.

import boto3
from aws_xray_sdk.core import xray_recorder
from aws_xray_sdk.core import patch

patch(['boto3'])

s3_client = boto3.client('s3')

def lambda_handler(event, context):
    bucket_name = event['bucket_name']
    bucket_key = event['bucket_key']
    body = event['body']

    put_object_into_s3(bucket_name, bucket_key, body)
    get_object_from_s3(bucket_name, bucket_key)

# Define subsegments manually
def put_object_into_s3(bucket_name, bucket_key, body):
    try:
        xray_recorder.begin_subsegment('put_object')
        response = s3_client.put_object(Bucket=bucket_name, Key=bucket_key, Body=body)
        status_code = response['ResponseMetadata']['HTTPStatusCode']
        xray_recorder.current_subsegment().put_annotation('put_response', status_code)
    finally:
        xray_recorder.end_subsegment()

# Use decorators to automatically set the subsegments
@xray_recorder.capture('get_object')
def get_object_from_s3(bucket_name, bucket_key):
    response = s3_client.get_object(Bucket=bucket_name, Key=bucket_key)
    status_code = response['ResponseMetadata']['HTTPStatusCode']
    xray_recorder.current_subsegment().put_annotation('get_response', status_code)

Note
The X-Ray SDK for Python allows you to patch the following modules:
botocore boto3 requests sqlite3 mysql You can use patch_all() to patch all of them at once.

Following is what a trace emitted by the code preceding looks like (synchronous invocation):