feat(aws-lambda): added eventContextExtractor config option

[prsnca]

Which problem is this PR solving?

• Today, Lambda instrumentation supports trace propagation only for X-Ray or HTTP headers. This enhancement allows to add a custom configuration for extracting the context from incoming events to the Lambda function. This will allow the instrumentation to support more event types, such as SQS, CloudWatch or Kinesis.

Short description of the changes

• Added eventContextExtractor config option to allow custom handling of events which carry the context in different ways. If not provided, a default context extractor is used and tries to pull the context from the HTTP headers - same as the behavior today.

[codecov]

Codecov Report

Merging #566 (297e26d) into main (902c91f) will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #566      +/-   ##
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- Coverage   94.77%   94.72%   -0.05%     
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  Files         179      174       -5     
  Lines       10921    10822      -99     
  Branches     1083     1057      -26     
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- Hits        10350    10251      -99     
  Misses        571      571              

Impacted Files	Coverage Δ
...-instrumentation-aws-lambda/src/instrumentation.ts	91.60% <0.00%> (-0.19%)	⬇️
...entation-document-load/src/enums/AttributeNames.ts
...strumentation-document-load/src/instrumentation.ts
...lemetry-instrumentation-document-load/src/utils.ts
...metry-instrumentation-document-load/src/version.ts
...trumentation-document-load/src/enums/EventNames.ts
...ws-lambda/test/integrations/lambda-handler.test.ts	97.97% <0.00%> (+0.09%)	⬆️

[vmarchaud]

lgtm, i tagged AWS people so they can check too

[willarmiros]

Thanks for the addition! Generally LGTM as well, but can you explain a bit more how context would be extracted from those event types other than an HTTP header? I assume it's for context propagation for vendors other than X-Ray since we don't have any special context stored in e.g. Kinesis/CW Events. But perhaps a small example code in the readme or unit test for what the custom extractors would look like would help me greatly.

[obecny]

2 things, with the rest will wait for creator of this instrumentation

[anuraaga]

LGTM with others' comments, thanks!

[prsnca]

Thanks for the addition! Generally LGTM as well, but can you explain a bit more how context would be extracted from those event types other than an HTTP header? I assume it's for context propagation for vendors other than X-Ray since we don't have any special context stored in e.g. Kinesis/CW Events. But perhaps a small example code in the readme or unit test for what the custom extractors would look like would help me greatly.

Sure!
One example could be a SQS message which triggers the Lambda function, where the trace header is found under the message attributes.
The event payload for the Lambda invocation would look as follows:

{
    "Records":
    [
        {
            "body": "someBody",
            "receiptHandle": "someReceiptHandler",
            "md5OfBody": "somemd5value",
            "eventSourceARN": "arn:aws:sqs:us-east-1:000000000000:0a1b2c3e4d5f",
            "eventSource": "aws:sqs",
            "awsRegion": "us-east-1",
            "messageId": "2c45653f-43ad-87e0-947e-074da0a1b45d",
            "attributes":
            {},
            "messageAttributes":
            {
                "traceparent":
                {
                    "stringValue": "00-c0f3ad06b7d55d5f91e1b5cdf32a63aa-002e02c5e90f1e34-01",
                    "dataType": "String"
                }
            },
            "md5OfMessageAttributes": "somemd5hash",
            "sqs": true
        }
    ]
}

The custom context extractor would be able to catch such cases and extract the context from the event.

[willarmiros]

lgtm as well, thanks for the walkthrough @prsnca!

[obecny]

Please don't force push after any first review / comment

[prsnca]

Please don't force push after any first review / comment

Sure! Thanks for the comment.
Could you please merge this PR?

[NikunjShah]

Have a question regarding this.How will the context be propagated in terms of SQS batching or other services which support batching. As the context can be fetched for a single message at a single point of time.

[nozik]

@NikunjShah That's a great question. You could handle that in several ways:

1. Iterate the Records array and create a consumer span for each message (but the handling of the message will appear as a separate trace)
2. Patch the iteration functions of the Records array (forEach / map / filter) and so that each iteration handler creates a span with the context of the handled message. This is possible in Node, and not really in other languages (and does have limitations, like no support for a "regular" for loop which cannot be patched
3. You could provide a decorator function that's inserted manually to each iteration in the code