Distributed Tracing with OpenTelemetry Spans

In a microservices system one user request can hop across an API gateway, an orders service, a payments service, and a database. When that request is slow, a single service's logs cannot tell you where the time went.

Distributed tracing stitches the whole journey together. Each unit of work becomes a span, spans are linked into a trace, and the trace reveals latency across every service boundary.

• Trace: the entire end-to-end request, identified by a traceId.
• Span: one operation (an HTTP call, a DB query) with a start time, duration, and parent.
• Context propagation: passing traceId and spanId across service boundaries, usually via HTTP headers.

OpenTelemetry (OTel) is the vendor-neutral standard for producing these spans in Node.js.

A span is the atomic building block of a trace. Every span carries the same trace identity but its own identity and timing.

• traceId: 16 bytes, shared by every span in the trace.
• spanId: 8 bytes, unique to this span.
• parentSpanId: links this span to the operation that caused it.
• name, startTime, endTime (duration = end - start).
• Attributes: key/value tags like http.method or db.system.
• Status: OK, ERROR, or UNSET.

Parent/child links form a tree. The root span is the whole request; child spans are the calls it makes. Visualized, the tree becomes the familiar waterfall you see in Jaeger or Tempo.