opentelemetry-java-instrumentation/declarative-config-bridge

Declarative Config Bridge

Declarative Config Bridge allows instrumentation authors to access configuration in a uniform way, regardless of the configuration source.

The bridge allows you to read configuration using the system property style when dealing with declarative configuration.

Example

As an example, let's look at the inferred spans configuration. First, there is a configuration method that reads the properties and is unaware of the source of the configuration:

class InferredSpansConfig {
  static SpanProcessor create(ConfigProperties properties) {
    // read properties here
    boolean backupDiagnosticFiles =
        properties.getBoolean("otel.inferred.spans.backup.diagnostic.files", false);
  }
}

The auto configuration without declarative config passes the provided properties directly:

@AutoService(AutoConfigurationCustomizerProvider.class)
public class InferredSpansAutoConfig implements AutoConfigurationCustomizerProvider {

  @Override
  public void customize(AutoConfigurationCustomizer config) {
    config.addTracerProviderCustomizer(
        (providerBuilder, properties) -> {
          providerBuilder.addSpanProcessor(InferredSpansConfig.create(properties));
          return providerBuilder;
        });
  }
}

The auto configuration with declarative config uses the Declarative Config Bridge to be able to use common configuration method:

Let's first look at the yaml file that is used to configure the inferred spans processor:

file_format: 1.0-rc.1
tracer_provider:
  processors:
    - inferred_spans:
        backup:
          diagnostic:
            files: true

And now the component provider that uses the Declarative Config Bridge:

@AutoService(ComponentProvider.class)
public class InferredSpansComponentProvider implements ComponentProvider<SpanProcessor> {

  @Override
  public String getName() {
    return "inferred_spans";
  }

  @Override
  public SpanProcessor create(DeclarativeConfigProperties config) {
    return InferredSpansConfig.create(
        new DeclarativeConfigPropertiesBridgeBuilder()
            // crop the prefix, because the properties are under the "inferred_spans" processor
            .addMapping("otel.inferred.spans.", "")
            .build(config));
  }

  @Override
  public Class<SpanProcessor> getType() {
    return SpanProcessor.class;
  }
}