How does distributed tracing work? What are Span and Trace ID?

Why Distributed Tracing Is Needed

In a microservices architecture, a single user request might traverse 10 services. When a request fails or slows down, traditional logs only show fragments from each service — hard to piece together the full path. Distributed tracing solves this.

Core Concepts

Trace: Represents the end-to-end path of a complete request, identified by a unique Trace ID.

Span: A unit of work within a trace, recording:

• Operation name
• Start/end time (to calculate latency)
• Status (success/failure)
• Tags (HTTP method, DB query, etc.)
• Parent Span ID (to build tree structure)

Context Propagation: Trace ID and Parent Span ID are passed between services via HTTP headers (W3C Trace Context standard: traceparent header).

Trace Visualization

A request trace is typically displayed as a Gantt chart:

• Horizontal axis is time
• Each service's Span appears as a horizontal bar
• Clearly shows which service took the most time

OpenTelemetry

An open standard that unifies the collection API and SDK for Metrics, Logs, and Traces.

Benefits: Vendor-neutral, not tied to any specific backend (can export to Jaeger, Zipkin, Grafana Tempo)

Implementation Note

Correlation ID strategy: Generate a Trace ID when a request enters the system and include it as a structured field in all logs — so even without a dedicated tracing tool, you can search logs by Trace ID.