feat(rum): propagate sampling decision through tracestate

[vigneshshanmugam]

• fix Record sampling weight to transactions/spans and propagate #845
• Adds a new option propagateTracestate boolean to optionally add the tracestate header to all outgoing requests from the browser that are captured as transactions and spans .
• sent as sample_rate and sr in both v2 and v3 spec in the APM server.
• Updated the config doc and also CORS docs.

[apmmachine]

📦 Bundlesize report

Filename	Size(bundled)	Size(gzip)	Diff(gzip)
elastic-apm-opentracing.umd.min.js	62.2 KiB	19.8 KiB	⚠️ 147 Bytes
elastic-apm-rum.umd.min.js	56.3 KiB	18.4 KiB	⚠️ 142 Bytes

[apmmachine]

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Build stats

• Build Cause: Pull request #953 updated

• • Start Time: 2021-02-01T19:41:48.336+0000

• Duration: 68 min 17 sec

• Commit: ee3e110

Test stats 🧪

Test	Results
Failed	0
Passed	1037
Skipped	13
Total	1050

Steps errors

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Run tests: Elastic Stack 7.0.0 - @elastic/apm-rum - none

• Took 3 min 13 sec . View more details on here

Run tests: Elastic Stack 8.0.0-SNAPSHOT - @elastic/apm-rum-core - saucelabs

• Took 6 min 57 sec . View more details on here

Error signal

• Took 0 min 0 sec . View more details on here

[hmdhk]

Thanks @vigneshshanmugam , a few points:

• I think we still need some validation for tracestate to avoid sending a large header by mistake or a similar bug (Also adding a test for this)
• The tests are failing at the moment
• I will review the spec in a bit more detail and give this another review.

[vigneshshanmugam]

@jahtalab I have added minimum validation for the values that we set, i think it should good to catch bugs that can arise due to bad sampling value. Also added and fixed the tests.

[hmdhk]

@vigneshshanmugam , I've added a few comments:

The spec mentions this as well, which is currently missing:

For non-sampled transactions set the transaction attributes sampled: false and sample_rate: 0, and omit context. No spans should be captured.

Also, the spec mentions storing the sampe_rate on spans as well, are we relying on apm-server to do this?

Agents will record the sampling rate on transactions and spans as sample_rate

[vigneshshanmugam]

Also, the spec mentions storing the sampe_rate on spans as well, are we relying on apm-server to do this?

I spoke with Server team yesterday and we would have to do this in the agent side for now as they cant infer in v2 API. I will change the code to propagate the info for spans.

[hmdhk]

@vigneshshanmugam , would you please take a look at the failing tests as well?

[hmdhk]

LGTM