Instrumenting AWS Lambda

Status: Experimental

This document defines how to apply semantic conventions when instrumenting an AWS Lambda request handler. AWS Lambda largely follows the conventions for FaaS while HTTP conventions are also applicable when handlers are for HTTP requests.

There are a variety of triggers for Lambda functions, and this document will grow over time to cover all the use cases.

All triggers

For all events, a span with kind SERVER SHOULD be created corresponding to the function invocation unless stated otherwise below. Unless stated otherwise below, the name of the span MUST be set to the function name from the Lambda Context.

The following attributes SHOULD be set:

• faas.invocation_id - The value of the AWS Request ID, which is always available through an accessor on the Lambda Context.
• cloud.account.id - In some languages, this is available as an accessor on the Lambda Context. Otherwise, it can be parsed from the ARN as the fifth item when splitting on :

Also consider setting other attributes of the faas resource and trace conventions and the cloud resource conventions. The following AWS Lambda-specific attribute MAY also be set:

Attribute	Type	Description	Examples	Requirement Level	Stability
aws.lambda.invoked_arn	string	The full invoked ARN as provided on the Context passed to the function (Lambda-Runtime-Invoked-Function-Arn header on the /runtime/invocation/next applicable). [1]	arn:aws:lambda:us-east-1:123456:function:myfunction:myalias	Recommended

[1] aws.lambda.invoked_arn: This may be different from cloud.resource_id if an alias is involved.

AWS X-Ray Active Tracing Considerations

When AWS X-Ray Active Tracing is enabled for a Lambda, the runtime will automatically generate a span based on configured sampling rates and propagate the span context via the _X_AMZN_TRACE_ID environment variable (and the com.amazonaws.xray.traceHeader system property for Java Lambda functions). This span context is encoded using the X-Ray Tracing Header Format.

Users MUST be able to configure the propagator to prioritize propagating this X-Ray “Active Tracing” span context. (FYI: Users probably want this enabled if OpenTelemetry is configured to report spans to AWS X-Ray so their trace is linked together properly.)

xray-lambda Propagator Functionality

SDK’s that have instrumentation for AWS Lambda SHOULD provide an additional propagator alongside the X-Ray propagator that can be configured via the OTEL_PROPAGATORS environment variable setting as xray-lambda. This propagator is expected to replace the xray propagator in the OTEL_PROPAGATORS list. The behavior for this propagator is described in pseudo code below.

extract(context, carrier) {
    xrayContext = xrayPropagator.extract(context, carrier)

    // To avoid potential issues when extracting with an active span context (such as with a span link),
    // the `xray-lambda` propagator SHOULD check if the provided context already has an active span context.
    // If found, the propagator SHOULD just return the extract result of the `xray` propagator.
    if (Span.fromContext(context).getSpanContext().isValid())
      return xrayContext

    // If xray-lambda environment variable not set, return the xray extract result.
    traceHeader = getEnvironment("_X_AMZN_TRACE_ID")
    if (isEmptyOrNull(traceHeader))
      return xrayContext

    // Apply the xray propagator using the span context contained in the xray-lambda environment variable.
    return xrayPropagator.extract(xrayContext, ["X-Amzn-Trace-Id": traceHeader])
}

Note: Java implementations should use the system property value of the key com.amazonaws.xray.traceHeader instead of the environment variable if the system property is not empty.

xray-lambda Propagator Configuration

When reporting spans to AWS X-Ray from AWS Lambda, the xray-lambda propagator SHOULD replace the xray propagator in the OTEL_PROPAGATORS configuration. Including both will prevent xray-lambda from functioning properly.

Example valid configuration when reporting spans to AWS X-Ray:

• OTEL_PROPAGATORS=tracecontext,baggage,xray-lambda

Example invalid configurations:

• OTEL_PROPAGATORS=tracecontext,baggage,xray,xray-lambda
• OTEL_PROPAGATORS=tracecontext,baggage,xray-lambda,xray

When OpenTelemetry is reporting traces to another system besides AWS X-Ray, users SHOULD NOT use xray-lambda or reported traces will be broken.

Example valid configuration when OpenTelemetry is reporting traces to another system besides AWS X-Ray:

• OTEL_PROPAGATORS=tracecontext,baggage,xray

API Gateway

API Gateway allows a user to trigger a Lambda function in response to HTTP requests. It can be configured to be a pure proxy, where the information about the original HTTP request is passed to the Lambda function, or as a configuration for a REST API, in which case only a deserialized body payload is available. In the case the API gateway is configured to proxy to the Lambda function, the instrumented request handler will have access to all the information about the HTTP request in the form of an API Gateway Proxy Request Event.

The Lambda span name and the http.route span attribute SHOULD be set to the resource property from the proxy request event, which corresponds to the user configured HTTP route instead of the function name.

faas.trigger MUST be set to http. HTTP attributes SHOULD be set based on the available information in the Lambda event initiated by the proxy request. http.scheme is available as the x-forwarded-proto header in the Lambda event. Refer to the input event format for more details.

SQS

Amazon Simple Queue Service (SQS) is a message queue that triggers a Lambda function with a batch of messages. So we consider processing both of a batch and of each individual message. The function invocation span MUST correspond to the SQS event, which is the batch of messages. For each message, an additional span SHOULD be created to correspond with the handling of the SQS message. Because handling of a message will be inside user business logic, not the Lambda framework, automatic instrumentation mechanisms without code change will often not be able to instrument the processing of the individual messages. Instrumentation SHOULD provide utilities for creating message processing spans within user code.

The span kind for both types of SQS spans SHOULD be CONSUMER.

SQS Event

For the SQS event span, if all the messages in the event have the same event source, the name of the span MUST be <event source> process. If there are multiple sources in the batch, the name MUST be multiple_sources process. The parent SHOULD be the SERVER span corresponding to the function invocation.

For every message in the event, the message system attributes (not message attributes, which are provided by the user) SHOULD be checked for the key AWSTraceHeader. If it is present, an OpenTelemetry Context SHOULD be parsed from the value of the attribute using the AWS X-Ray Propagator and added as a link to the span. This means the span may have as many links as messages in the batch. See compatibility for more info.

• faas.trigger MUST be set to pubsub.
• messaging.operation.type MUST be set to process.
• messaging.system MUST be set to aws_sqs.

SQS Message

For the SQS message span, the name MUST be <event source> process. The parent MUST be the CONSUMER span corresponding to the SQS event. The message system attributes (not message attributes, which are provided by the user) SHOULD be checked for the key AWSTraceHeader. If it is present, an OpenTelemetry Context SHOULD be parsed from the value of the attribute using the AWS X-Ray Propagator and added as a link to the span. See compatibility for more info.

• faas.trigger MUST be set to pubsub.
• messaging.operation.type MUST be set to process.
• messaging.system MUST be set to aws_sqs.

Other Messaging attributes SHOULD be set based on the available information in the SQS message event.

Note that AWSTraceHeader is the only supported mechanism for propagating Context in instrumentation for SQS to prevent conflicts with other sources. Notably, message attributes (user-provided, not system) are not supported - the linked contexts are always expected to have been sent as HTTP headers of the SQS.SendMessage request that the message originated from. This is a function of AWS SDK instrumentation, not Lambda instrumentation.

Using the AWSTraceHeader ensures that propagation will work across AWS services that may be integrated to Lambda via SQS, for example a flow that goes through S3 -> SNS -> SQS -> Lambda. AWSTraceHeader is only a means of propagating context and not tied to any particular observability backend. Notably, using it does not imply using AWS X-Ray - any observability backend will fully function using this propagation mechanism.

Examples

API Gateway Request Proxy (Lambda tracing passive)

Given a process C that sends an HTTP request to an API Gateway endpoint with path /pets/{petId} configured for a Lambda function F:

Process C: | Span Client        |
--
Function F:    | Span Function |

API Gateway Request Proxy (Lambda tracing active)

Active tracing in Lambda means an API Gateway span Span APIGW and a Lambda runtime invocation span Span Lambda will be exported to AWS X-Ray by the infrastructure (not instrumentation). All attributes above are the same except that in this case, the parent of APIGW is Span Client and the parent of Span Function is Span Lambda. This means the hierarchy looks like:

Span Client --> Span APIGW --> Span Lambda --> Span Function

SQS (Lambda tracing passive)

Given a process P, that sends two messages to a queue Q on SQS, and a Lambda function F, which processes both of them in one batch (Span ProcBatch) and generates a processing span for each message separately (Spans Proc1 and Proc2).

Process P: | Span Prod1 | Span Prod2 |
--
Function F:                      | Span ProcBatch |
                                        | Span Proc1 |
                                               | Span Proc2 |

Note that if Span Prod1 and Span Prod2 were sent to different queues, Span ProcBatch would not have messaging.destination.name set as it would correspond to multiple queues.

The above requires user code change to create Span Proc1 and Span Proc2. In Java, the user would inherit from TracingSqsMessageHandler instead of Lambda’s standard RequestHandler to enable them. Otherwise these two spans would not exist.

SQS (Lambda tracing active)

Active tracing in Lambda means a Lambda runtime invocation span Span Lambda will be exported to X-Ray by the infrastructure (not instrumentation). In this case, all of the above is the same except Span ProcBatch will have a parent of Span Lambda. This means the hierarchy looks like:

Span Lambda --> Span ProcBatch --> Span Proc1 (links to Span Prod1 and Span Prod2)
                               \-> Span Proc2 (links to Span Prod1 and Span Prod2)

Resource Detector

AWS Lambda resource information is available as environment variables provided by the runtime.

• cloud.provider MUST be set to aws
• cloud.region MUST be set to the value of the AWS_REGION environment variable
• faas.name MUST be set to the value of the AWS_LAMBDA_FUNCTION_NAME environment variable
• faas.version MUST be set to the value of the AWS_LAMBDA_FUNCTION_VERSION environment variable

Note that cloud.resource_id currently cannot be populated as a resource because it is not available until function invocation.