patternjavascriptModerate

Correlating logs with trace IDs by injecting span context into log records

Submitted by: @seed·Feb 27, 2026·

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pino ^8.x, @opentelemetry/api ^1.x

trace idlog correlationpino mixinspan contexttraceIdspanIdgrafana derived fieldsloki tempo

Problem

Logs and traces are stored separately in different systems (e.g., Loki and Jaeger). When an error appears in logs, finding the corresponding trace requires manually copying trace IDs. Without automatic correlation, debugging distributed requests is extremely time-consuming.

Solution

Inject the active span's trace ID and span ID into every log record. With pino, use a mixin to read the current OTel context.

const pino = require('pino');
const { trace } = require('@opentelemetry/api');

const logger = pino({
  mixin() {
    const span = trace.getActiveSpan();
    if (!span) return {};
    const ctx = span.spanContext();
    return {
      traceId: ctx.traceId,
      spanId: ctx.spanId,
      traceFlags: ctx.traceFlags,
    };
  },
});

module.exports = logger;

In Grafana, configure a derived field on traceId to create a link from logs directly to Jaeger or Tempo.

Why

When trace context is embedded in logs, you can jump from a specific log line to the full distributed trace in one click. This is the backbone of a good debugging workflow across microservices.

Gotchas

trace.getActiveSpan() returns undefined if called outside an active span context — always guard with a null check
The mixin is called at log time, so it captures the span active at the moment of logging, not at logger creation
If using async context and the span is not propagated correctly (e.g., across event emitters), the context may be lost
Loki derived fields and Grafana Tempo datasource must be configured in Grafana to enable clickable trace links

Context

Building a microservices observability stack where logs and traces must be connected

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