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To correlate application logs with distributed traces, emit structured log records and include the active trace ID and span ID when available. Keep your existing logging library if it has a supported OpenTelemetry integration; replacing it is not a prerequisite. OpenTelemetry can then carry logs through a Collector for consistent processing and enrichment before they reach a telemetry backend.
What structured logging adds beyond console.log
A plain console.log call commonly produces a rendered string. If a message says payment failed for order 42, a person can read it, but a search or processing system may have to parse the prose to separate the event, order, and outcome.
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A structured log represents an event as a record with distinct fields. For example, an event might carry an event name, an order identifier, and an outcome as separate attributes. That makes attributes available for consistent processing and querying instead of embedding the only copy of each value in a string. JSON-looking text is not automatically structured logging: the important distinction is whether the logging pipeline treats the values as record fields.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsOpenTelemetry defines a log data model and semantic conventions for structured events. Its logging support is designed to work with existing logging libraries as well as the wider observability ecosystem. See OpenTelemetry’s logging specification and overview of its telemetry model.
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How trace context connects logs to a request
A distributed trace follows work across services. It consists of spans that represent operations along the way. The trace ID identifies the distributed trace; a span ID identifies an individual span within it. OpenTelemetry’s SpanContext carries the trace ID, span ID, trace flags, and trace state, and conforms to W3C Trace Context. The OpenTelemetry Tracing API describes the span context.
For spans from separate services to form one coherent trace, the trace context has to propagate across service boundaries. For HTTP, W3C Trace Context specifies standard headers and a value format for that propagation. As the W3C Distributed Tracing Working Group puts it, “This specification defines standard HTTP headers and a value format to propagate context information that enables distributed tracing scenarios.” Read the W3C Trace Context Recommendation.
When a log is emitted while a span is active, include its trace ID and span ID in the log record when the logging integration supports it. Those identifiers let a user navigate from the log to the relevant trace and connect logs from different components involved in the same request. A trace ID groups the distributed work; a span ID locates the particular operation associated with that log.
What to put in a useful log record
Keep the event’s meaning and context in explicit fields rather than relying on a sentence that must be parsed. A practical record should distinguish the event attributes from the identity and context of the process that emitted it.
- Event attributes: fields describing what happened, such as an event name, outcome, or relevant application identifier. Use consistent names and types so queries and processors can treat the fields consistently.
- Trace context: the active trace ID and span ID when available. These connect the record to a particular trace and operation.
- Resource context: information identifying the telemetry-producing entity, such as the service or host. OpenTelemetry’s Resource context helps identify where telemetry originated; it complements rather than replaces trace context.
- Event time: time can help correlate a log with telemetry, but time-based proximity is not as precise as carrying trace and span identifiers.
Not every log has an active span. Legacy or system logs may have no trace context, so they cannot always be precisely correlated with a trace. Resource enrichment can still identify their origin, for example a host or container. OpenTelemetry discusses log correlation and resource context in its logging specification and overview.
Choose how to connect your logging library to OpenTelemetry
There are two broad paths: retain an existing logging library and connect it to OpenTelemetry, or emit records through the OpenTelemetry Logs API. The right choice depends on the language and framework support available, the event structure you need, and the logging features your application already uses.
| Approach | What it means | What to evaluate |
|---|---|---|
| Keep the existing logging library | Connect it using an OpenTelemetry appender or instrumentation where available. | Check language and framework support, whether trace context is injected, how existing logging features are retained, and how much integration configuration operations must maintain. |
| Emit through the OpenTelemetry Logs API | Use the API directly to emit structured log records or events. | Assess control over event structure, the support available in your language and framework, and whether the API supplies the logging features your application needs. |
OpenTelemetry notes that existing logging libraries generally provide richer features than the Logs API. That makes integration a sensible first option when it is supported and meets your requirements; an API change should be a deliberate choice, not an assumed prerequisite. Availability differs across languages and frameworks, so verify the integration for your stack in the OpenTelemetry logging documentation.
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Adopt structured logs and trace correlation in stages
- Inventory how logs are produced. Identify the application logging libraries, relevant languages and frameworks, and any legacy or system-log sources. Separate application events that can run inside a span from records that have no request context.
- Choose the integration path. Check for supported OpenTelemetry appenders or instrumentation for the existing library. If that path is unavailable or does not meet your event-structure needs, evaluate emitting through the OpenTelemetry Logs API.
- Define consistent event fields. Decide which attributes describe each important event and apply consistent names and types. Prefer fields that a query can address directly over values buried in prose.
- Propagate trace context across services. Ensure the HTTP path uses W3C Trace Context propagation so spans created by separate services can join the same distributed trace.
- Attach active trace identifiers to logs. Configure the integration or emission code to capture the current trace and span IDs when a span is active. Verify that the IDs on a log match the trace and operation expected for that request.
- Preserve resource identity. Enrich telemetry with resource information that identifies its producer, such as service or host, so logs without trace context can still be attributed to an origin.
- Route and inspect the data. Send logs through your telemetry pipeline and confirm that event attributes, resource information, and trace identifiers remain distinct and searchable at the destination.
What the OpenTelemetry Collector contributes
The Collector can provide a uniform place to receive, enrich, and process telemetry before forwarding it to a backend. For logs, this creates a central processing stage rather than requiring every application to implement the same downstream handling. A deployment can send logs through the Collector and onward to a backend, while preserving the structured fields and context needed for querying and trace correlation.
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The Collector does not create trace context retroactively for records that were emitted without it. Legacy and system logs can still benefit from resource enrichment, but their origin information is not a substitute for the trace and span IDs that connect an application event to a specific operation. OpenTelemetry describes logging and integration with its ecosystem in the logging specification.
Quick Recap
Common failure points to check
- Fields are only embedded in a message string. Confirm that the output pipeline retains event attributes as separate fields rather than requiring downstream parsing of prose.
- Trace IDs appear in some services but not others. Check both context propagation across HTTP boundaries and whether each service’s logging integration reads the active span context.
- Logs have trace IDs but are hard to attribute. Add or verify Resource context identifying the telemetry-producing service or host.
- Older logs cannot be opened from a trace. If they were emitted without active trace context, precise trace correlation may not be possible after the fact; use their timestamp and resource identity as available context.
- An integration is missing for your stack. Confirm language and framework support before selecting an appender or instrumentation, and consider the Logs API only after weighing its feature and operational trade-offs.
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