Distributed tracing
- Node.js course
- Expert
- Lesson 33/47
- 5 min
Learn distributed tracing with OpenTelemetry.
Distributed tracing
Distributed tracing gathers a request's path across many services into one view. OpenTelemetry is the open standard that collects traces uniformly. Each trace gets a trace ID, each step a span ID.
A traceContext(traceId, spanId) function models this link: it joins the two ids with ':'. Example: traceContext('abc123', 'span01') returns 'abc123:span01'. In real OpenTelemetry this context propagates through HTTP headers; here we only see how the ids pair up. The trace ID ties the whole request; the span ID marks a step. This split is what lets you find one request's path among millions of logs.
Context propagation
A trace context propagates across services through HTTP headers. OpenTelemetry's traceparent header carries it in the form 00-<traceId>-<spanId>-<flags>. Each service reads the incoming context, adds its own span and forwards it.
In our simple model traceContext('abc123', 'span01') returns 'abc123:span01'; the real traceparent header would be 00-abc123-span01-01. Joining the two ids shows the structure of the context; the full header format comes later. This model captures the heart of distributed tracing: chaining every step under a single trace ID. This is how you quickly find which service caused a failure.
Practice Write the trace context function
Write function traceContext(traceId, spanId). Return traceId + ':' + spanId. Print console.log(traceContext('abc123', 'span01')).
Starter code
// Write the traceContext function
// Join the two ids with ':' and return
// Call with 'abc123' and 'span01', print
// write hereSample solution
function traceContext(traceId, spanId) {
return traceId + ':' + spanId;
}
console.log(traceContext('abc123', 'span01'));Expected output
abc123:span01
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match each piece to its role
| Term | Meaning |
|---|---|
trace ID |
Ties the request |
span ID |
Marks a step |
OpenTelemetry |
Open standard |
traceContext |
Joins ids |
2 What is a trace associated with in OpenTelemetry?
traceContext('abc123', 'span01')- Only the span
- Trace ID ve span ID Correct answer
- Only the flag
- Only the context
Explanation: A trace is associated with a trace ID and a span ID.
3 Complete the join separator
return traceId + '____' + spanId;return traceId + ':' + spanId;Explanation: The two ids are joined with ':'.