[Sampler.AWS] Wrapped root sampler with ParentBasedSampler

[AsakerMohd]

Fixes #
Design discussion issue #

Changes

The current implementation of the X-Ray sampler has 2 levels: The X-Ray Sampler itself which is made up two different samplers for X-Ray purposes. Those two different samplers are wrapped by parentBasedSampler so that the children inherit the parent sampling decision. However, on the CloudWatch console, we are adding the children sampling decision into the stats section. This means: if we have 1 parent and 9 children, the CW console will show that 10 spans are sampled which isn't correct. It should show only 1 span being sampled. This PR moves the ParentBasedSampler wrapper to be on the root level of the X-Ray sampler. This means that the builder doesn't return AWSXrayRemoteSampler anymore but returns ParentBasedSampler(new AWSXrayRemoteSampler). This keeps the same parentBasedSampling logic but is instead on the root level thus skipping the stat aggregation for the children.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[vastin]

LGTM

[Kielek]

Suggested change

	public ParentBasedSampler Build()
	public Sampler Build()

Shouldn't it be just Sampler to avoid any future breaking changes?

[AsakerMohd]

Good call. Updated the return type to be Trace.Sampler instead of ParentBasedSampler.

[ppittle]

Is there a way to avoid needing a special constructor just for testing?

Could the tests call Build, get the ParentBasedSampler and then access the AWSXrayRemoteSampler from that class some way?

[AsakerMohd]

Using reflection allows us to get the private sampler in the ParentBasedSampler class. However doing so is kindoff a code smell since at this point we are relying on the internal variable naming of ParentBasedSampler and if that changes, the test breaks. I would prefer using the special constructor in this case since it's being used in the actual public facing Build function and can be used to test the AWSXrayRemoteSampler being built properly.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review.

Project coverage is 87.28%. Comparing base (71655ce) to head (a5efb24).
Report is 539 commits behind head on main.

Files with missing lines	Patch %	Lines
...lemetry.Sampler.AWS/AWSXRayRemoteSamplerBuilder.cs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2188       +/-   ##
===========================================
+ Coverage   73.91%   87.28%   +13.36%     
===========================================
  Files         267       20      -247     
  Lines        9615      574     -9041     
===========================================
- Hits         7107      501     -6606     
+ Misses       2508       73     -2435     

Flag	Coverage Δ
unittests-Sampler.AWS	87.28% <66.66%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/OpenTelemetry.Sampler.AWS/FallbackSampler.cs	55.55% <100.00%> (ø)
...c/OpenTelemetry.Sampler.AWS/SamplingRuleApplier.cs	98.56% <100.00%> (ø)
...lemetry.Sampler.AWS/AWSXRayRemoteSamplerBuilder.cs	70.00% <0.00%> (-12.36%)	⬇️

... and 261 files with indirect coverage changes