Span start/end after parent and trans end should be allowed

[trentm]

An APM agent shouldn't prevent the creation/start of a span after its parent or its containing transaction has ended.

FWIW, the Java APM agent (I'm told) already allows span creation and end after its parent and transaction have ended.

Motivation

It is possible (at least in Node.js) to have a span creation/start happen after its containing transaction has already ended. With the OTel API this can happen like this:

const otel = require('@opentelemetry/api')
const tracer = otel.trace.getTracer('play')

// Create an OTel span "s1" with the OTel API. Here we create Transaction "s1".
const s1 = tracer.startSpan('s1')
const ctx1 = otel.trace.setSpan(otel.context.active(), s1)

// The edge case: Create a child of "s1" after s1 has *ended*.
// - When using the OTel SDK: This works. s4 is a child of s1.
// - When using the Elastic OTel Bridge: This results in an *attempt* to create
//   a child Span of s1, but that returns `null` with the debug log:
//        DEBUG: transaction already ended - cannot build new span
s1.end()
const s4 = tracer.startSpan('s4', {}, ctx1)
s4.end()

This "transaction already ended - cannot build new span" limitation in the current Node.js APM agent dates back to v1 of the APM Server intake API when all of a transaction's spans had to be reported with the transaction -- and that was done on transaction end. The v2 intake API no longer requires this. elastic/apm-agent-nodejs#2653 will be removing this restriction in the Node.js APM agent.

checklist

• May the instrumentation collect sensitive information, such as secrets or PII (ex. in headers)?
  • Yes
    • Add a section to the spec how agents should apply sanitization (such as sanitize_field_names)
  • No
    • Why?
  • n/a
• Create PR as draft
• Approval by at least one other agent
• Mark as Ready for Review (automatically requests reviews from all agents and PM via CODEOWNERS)
  • Remove PM from reviewers if impact on product is negligible
  • Remove agents from reviewers if the change is not relevant for them
• Approved by at least 2 agents + PM (if relevant)
• Merge after 7 days passed without objections
• Create implementation issues through the meta issue template (this will automate issue creation for individual agents)

[apmmachine]

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• Start Time: 2022-05-02T04:01:00.079+0000

• Duration: 3 min 1 sec

[jaggederest]

This could also happen in the case of e.g. a delayed promise that starts a span, right? I think this is logically fine. Edit: On behalf of APM Agent Ruby though my permissions may not be 100% correct to get github to automate it 👍

[trentm]

This could also happen in the case of e.g. a delayed promise that starts a span, right?

Yes. Or any async task like a setTimeout, as well.