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Document handling of empty OperationId in logs #128629

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10 changes: 10 additions & 0 deletions articles/azure-functions/opentelemetry-howto.md
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Expand Up @@ -617,6 +617,16 @@ Triggers such as HTTP, Service Bus, and Event Hubs depend on context propagation

In Azure Functions, the `OperationId` used for correlating telemetry comes directly from the `traceparent` value in the incoming request or message. If multiple calls reuse the same `traceparent` value, they all get the same `OperationId`.

### Application logs have an empty OperationId

Application logs written by your function code can appear in the traces table with an empty operation_Id. As a result, they don't correlate with the invocation's request and trace in the end-to-end transaction view.

As described in Duplicate OperationId, the operation_Id is applied to telemetry that is emitted within the invocation context. Application logs emitted outside that context—for example, logs that the Functions host forwards—are recorded without an operation_Id.

If you need OperationId in your application logs, use the Application Insights agent to instrument your logging framework instead of the OpenTelemetry mode: enable the agent as described in [Enable Azure Monitor OpenTelemetry for .NET, Node.js, Python, and Java applications](https://learn.microsoft.com/en-us/azure/azure-monitor/app/opentelemetry-enable?tabs=java). The agent stamps the trace context (operation_Id = trace ID) on the logs it emits within the invocation context.

@v-regandowner Regan Downer (v-regandowner) Jul 13, 2026

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If you need OperationId in your application logs, use the Application Insights agent to instrument your logging framework instead of the OpenTelemetry mode: enable the agent as described in [Enable Azure Monitor OpenTelemetry for .NET, Node.js, Python, and Java applications](https://learn.microsoft.com/en-us/azure/azure-monitor/app/opentelemetry-enable?tabs=java). The agent stamps the trace context (operation_Id = trace ID) on the logs it emits within the invocation context.
If you need OperationId in your application logs, use the Application Insights agent to instrument your logging framework instead of the OpenTelemetry mode: enable the agent as described in [Enable Azure Monitor OpenTelemetry for .NET, Node.js, Python, and Java applications](/azure/azure-monitor/app/opentelemetry-enable?tabs=java). The agent stamps the trace context (operation_Id = trace ID) on the logs it emits within the invocation context.

Comment on lines +622 to +626

Make sure telemetryMode isn't set to OpenTelemetry in your `host.json`. If you added `"telemetryMode": "OpenTelemetry"`, remove it.

### Configure OpenTelemetry with environment variables

You can configure OpenTelemetry behavior by using its standard environment variables. These variables provide a consistent way to control behavior across different languages and runtimes. You can adjust sampling strategies, exporter settings, and resource attributes. For more information about supported environment variables, see the [OpenTelemetry documentation](https://opentelemetry.io/docs/languages/sdk-configuration/).
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