The spec for file configuration is shaping up, opentelemetry-cpp needs to start planning for this.

• Configuration proposal oteps#225
• Define OTEL_CONFIG_FILE environment variable opentelemetry-specification#3805
• Define OTEL_CONFIG_FILE with environment variable merge semantics opentelemetry-specification#3840
• Define OTEL_CONFIG_FILE with placeholder for new environment variable override scheme opentelemetry-specification#3850
• Define OTEL_EXPERIMENTAL_CONFIG_FILE to ignore other env vars, add env var substitution default syntax opentelemetry-specification#3948
• Add spec compliance matrix entries for file configuration opentelemetry-specification#3804
• Define sdk extension component support in file configuration opentelemetry-specification#3802
• Should file configuration merge environment variable configuration? opentelemetry-specification#3752
• Deprecate environment variables which do not interoperate with file config when ready for stabilization opentelemetry-specification#3967
• Ensure that file config has solution for platforms which contribute to config opentelemetry-specification#3966

Spec: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/configuration/file-configuration.md

Sub tasks:

• Define the config file format (yaml)
• Define the config file schema - experimental, see https://github.com/open-telemetry/opentelemetry-configuration
• Pick a yaml parser
  • Evaluate yaml-cpp - DO NOT USE
  • Evaluate rapidyaml.
  • Evaluate other choices.
• Define C++ classes for the config model
  • Propagators.
  • Traces.
  • Metrics.
  • Logs.
• Implement environment variables substitution from yaml
• Populate the C++ config model from yaml
  • Propagators.
  • Traces.
  • Metrics.
  • Logs.
• Instantiate SDK and exporter objects from the C++ config model
  • Propagators.
  • Traces.
  • Metrics.
  • Logs.
• User documentation
• Define a registry for plugin components
  • propagators
  • trace plugins
    • samplers
    • span processors
    • span exporters
  • metric plugins
  • logs plugins
• Populate config model from yaml, for registered third party components
  • propagators
  • trace plugins
    • samplers
    • span processors
    • span exporters
  • metric plugins
  • logs plugins
• Instantiate plugins from config model, for registered third party components
  • propagators
  • trace plugins
    • samplers
    • span processors
    • span exporters
  • metric plugins
  • logs plugins
• Third party documentation (for implementing plugins)

Related issues, found while implementing this feature:

• opentelemetry-configuration
  • Add IdGenerator in tracer_provider opentelemetry-configuration#70
  • Improve key/value pairs in headers opentelemetry-configuration#72
  • Rename file_format to avoid confusion opentelemetry-configuration#74
  • Define schema for simple propagator opentelemetry-configuration#75
• opentelemetry-specifications
  • [file configuration] Clarify environment variable substitution is not recursive. opentelemetry-specification#3894
  • Clarify environment variable substitution is not recursive opentelemetry-specification#3913
  • [File configuration] Alternate proposal for config.yaml, including merges opentelemetry-specification#3920
• opentelemetry-cpp
  • [BUILD] Incorrect test on ENABLE_OTLP_GRPC_SSL_MTLS_PREVIEW #2545
  • [DOC] Guidelines for new software dependencies #2552
  • [API/SDK] Provider cleanup #2664