Observe Arc execution

Add the Arc observability starter alongside the Arc Spring Boot starter:

dependencies {
    implementation("io.cratis:arc-observability-spring-boot-starter:<version>")
}

The starter activates when the application provides a Micrometer ObservationRegistry. Spring Boot Actuator supplies one in a typical metrics or tracing application. Without a registry, with ObservationRegistry.NOOP, or when cratis.arc.observability.enabled=false, Arc leaves the existing pipeline beans unchanged.

Recorded operations

The starter decorates application-supplied or Arc-provided contracts without replacing their implementations:

Observation	Operations	Low-cardinality tags
arc.command	execute, validate	arc.operation, arc.artifact, arc.outcome
arc.query	perform	arc.operation, arc.query, arc.outcome
arc.observable.query	open, subscription, emission	arc.operation, arc.query, arc.outcome
arc.authentication	authenticate	arc.operation, arc.outcome
arc.identity.details	provide	arc.operation, arc.outcome

Outcome values are bounded categories such as success, invalid, unauthorized, not_ready, authenticated, anonymous, rejected, cancelled, and error. Thrown failures are attached to the observation so a tracing handler can mark the span as failed. Observable subscriptions remain active until completion, cancellation, or failure; each delivered result has a separate emission observation.

Arc never records command values, query arguments, tenant identifiers, user identifiers, claims, headers, or cookies. Command artifact types and generated query names are the only model-specific low-cardinality dimensions.

Correlation context

The correlation identifier itself is established by the Arc Spring Boot starter, not by this one. Its host-wide correlation filter resolves one identifier per request, publishes it to every route in the host, and places it in MDC under arc.correlation_id for the duration of the servlet filter chain. See the HTTP contract reference for that contract.

For command and query operations, Arc places the existing request correlation identifier in the observation context under arc.correlation_id. It is deliberately not a metric or span tag.

When SLF4J is available, the starter also places the value in MDC under arc.correlation_id for the duration of each coroutine resume, which is where the servlet-thread binding cannot reach. When the OpenTelemetry API is available, it places the same value in baggage. Both contexts are restored after execution, including cancellation and failure. This preserves structured coroutine propagation rather than relying on an unmanaged application ThreadLocal.

OpenTelemetry is optional. Add the tracing implementation appropriate for the application, for example Spring Boot Actuator with Micrometer’s OpenTelemetry bridge. The Arc starter does not select an exporter.

Configuration

cratis:
  arc:
    observability:
      enabled: true
      correlation-baggage-enabled: true
      correlation-logging-enabled: true

The properties are ordinary JavaBean configuration through ArcObservabilityProperties. Disable baggage or logging correlation independently when the host owns those contexts itself.