Add Micrometer distributed tracing (OTLP / Zipkin)

[piush365]

Background

Correlation IDs are propagated through MDC and response headers, but there is no span-level distributed trace. This makes it hard to visualise the latency breakdown across Redis → Kafka → PostgreSQL for a single request.

Proposed Change

Add Micrometer Tracing with an OTLP exporter so every order request produces a complete trace.

Dependencies

<dependency>
  <groupId>io.micrometer</groupId>
  <artifactId>micrometer-tracing-bridge-otel</artifactId>
</dependency>
<dependency>
  <groupId>io.opentelemetry</groupId>
  <artifactId>opentelemetry-exporter-otlp</artifactId>
</dependency>

Config

management:
  tracing:
    sampling:
      probability: 1.0
  otlp:
    tracing:
      endpoint: http://otel-collector:4318/v1/traces

Docker Compose additions

• OpenTelemetry Collector sidecar
• Jaeger UI for trace visualisation

Acceptance Criteria

• Every HTTP request produces a trace with spans for Redis, Kafka, and DB operations
• traceId appears in log lines alongside correlationId
• Jaeger UI added to docker-compose.yml
• README monitoring section updated with Jaeger URL