feat: AWS X-Ray Remote Sampler Part 3 - Add Rate Limiter and Sampling Targets Poller Logic

[jj22ee]

Description

• Followup PR of feat: AWS X-Ray Remote Sampler Part 2 - Add Rules Caching and Rules Matching Logic #1498

This is the 3rd and final PR to address #1434 in order for OTel Ruby to support X-Ray Remote Sampling.

Changes:

• Added logic to fetch sampling targets for each sampling_rule_applier.
  • The sampling targets are periodically fetched every 10 seconds by making the GetSamplingTargets API call to X-Ray.
  • The targets determine the reservoir quota and the rate at which a sampling_rule_applier will sample the requests.
  • Each rule applier keeps and updates a sampling statistics document which is required in GetSamplingTargets call to determine the next target
• Added a rate_limiting_sampler (applied before the fixed rate sampler) to be used in each rule applier.
  • Together these samplers determine how many requests to sample every second and what percentage of additional requests to sample in that second.
  • The fallback_sampler is updated to be a combination of above samplers to sample 1 req/sec and 5% of additional requests in that second.
• Added example/xray_sampling_on_rails_demonstration.ru that runs an example rails application that uses the OpenTelemetry X-Ray Sampler, with example instructions in the comments at the bottom of the file.

Testing

• Unit Tests
• The current implementation was tested against X-Ray's Centralized Sampling Integration tests.

[kaylareopelle]

Hi @jj22ee, thanks for your patience. I'll take a look at this PR later today. Will the new gem be ready for release after this PR?

[jj22ee]

Thanks @kaylareopelle! This new gem will be ready for releasing after this PR.