04-spring-classic-simple

04-spring-classic-simple

This project is showcasing Micrometer APIs using classic thread-per-request approach.

• build.gradle.kts
• spring-classic-simple.http
• HelloControllerV1.kt
• HelloControllerV2.kt
• HelloControllerV3.kt

How does it work?

io.micrometer:micrometer-tracing

• defines io.micrometer.tracing.handler.TracingObservationHandler that reacts to Observation lifecycle
• implements multiple versions of TracingObservationHandler, e.g. PropagatingReceiverTracingObservationHandler

io.micrometer:micrometer-tracing-bridge-brave

• a library implementing a set of abstractions from io.micrometer:micrometer-tracing via delegating to Brave tracer
• when this library is on the classpath, org.springframework.boot:spring-boot-actuator-autoconfigure will set up tracing via Brave
• autoconfiguration is done by org.springframework.boot.actuate.autoconfigure.tracing.BraveAutoConfiguration
• while also more configuration is loaded from org.springframework.boot.actuate.autoconfigure.tracing.BravePropagationConfigurations
• BraveAutoConfiguration sets up ThreadLocalCurrentTraceContext to allow for context propagation based on thread-locals
• and BravePropagationConfigurations will take care of adding MDCScopeDecorator to Brave Tracer

io.micrometer:micrometer-tracing-bridge-otel

• bridges to Otel tracer instead of Brave
• contains more code overall compared to Brave bridge (due to bigger diff between APIs)
• adding Baggage values to MDC is handled by Slf4JBaggageEventListener

HelloControllerV1

• Observation is created by org.springframework.web.filter.ServerHttpObservationFilter
• PropagatingReceiverTracingObservationHandler reacts to Observation getting created and creates a span via Tracer
• Observation is then put into scope by ServerHttpObservationFilter
• PropagatingReceiverTracingObservationHandler reacts to it and makes the associated span "current"