NLog Target for OpenTelemetry

This target can export logs in the format defined in the OpenTelemetry specification using the OpenTelemetry.Exporter.OpenTelemetryProtocol package.

For an explanation of the log data model, see https://opentelemetry.io/docs/specs/otel/logs/data-model/.
For an example, see https://opentelemetry.io/docs/specs/otel/protocol/file-exporter/#examples.

Note that the OpenTelemetry logging API is still unfinished, which means that it is internal in stable releases and public in prelease versions of the OpenTelemetry package. This package has a reference to OpenTelemetry version 1.9.0-alpha.1. If your project has a reference to a stable version higher than that, you will get a runtime error.

Configuration

Example XML config:

<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    
    <extensions>
        <add assembly="NLog.Targets.OpenTelemetryProtocol"/>
    </extensions>

    <targets>
      <target xsi:type="OtlpTarget"
        name="otlp"
        usehttp="true"
        servicename="TestService"
        scheduledDelayMilliseconds="1000"
        useDefaultResources="false"
        includeFormattedMessage="true"
        onlyIncldueParameters="correlationId,messageId">
          <attribute name="thread.id" layout="${threadid}" />
          <resource name="process.name" layout="${processname}" />
          <resource name="process.id" layout="${processid}" />
          <resource name="deployment.environment" layout="DEV" />
      </target>
    </targets>
    <rules>
        <logger name="*" writeTo="otlp" />
    </rules>
</nlog>

Configuration parameters

• Endpoint : Determines where the exporter should send logs. Used to set OtlpExporterOptions.Endpoint. When not specified it will use environment-variable: OTEL_EXPORTER_OTLP_ENDPOINT
• UseHttp : Determines whether logs are exported using gRPC or HTTP. (optional). By default false, where protocol is determined by environment-variable: OTEL_EXPORTER_OTLP_PROTOCOL
• Headers : Used to set OtlpExporterOptions.Headers (optional). When not specified it will use environment-variable: OTEL_EXPORTER_OTLP_HEADERS
• ServiceName : Used to set the service.name resource (optional). When not specified it will use environment-variable: OTEL_SERVICE_NAME
• UseDefaultResources : Use default resources like: telemetry.sdk.name, telemetry.sdk.language and telemetry.sdk.version. By default true, where resources are determined by environment-variable: OTEL_RESOURCE_ATTRIBUTES
• Resource : Additional resources to include in the ResourceBuilder (optional)
  • Name : Name of Resource.
  • Layout : Value of Resource (Will only resolve value at target initialize)
• Attribute : Attributes to be included with each LogEvent (optional)
  • Name : Name of Attribute.
  • Layout : Value of Attribute (If value is the same for all LogEvents, then add as resource instead)
• MaxQueueSize : The target uses a batch exporter, this defines the max queue size. By default 2048, optional.
• MaxExportBatchSize : The target uses a batch exporter, this defines the max batch size. By default 512, optional.
• ScheduledDelayMilliseconds : The target uses a batch exporter, this defines how often it is flushed in milliseconds. By default 5000, optional.
• IncludeFormattedMessage : If you're doing structured logging, this determines whether the body of the outputted log should be the formatted message or the message template. By default false, meaning the body of the outputted log will be the message template. If you aren't doing structured logging, leave this as false.
• IncludeEventProperties : If you're doing structured logging, this determines whether to include NLog LogEvent properties as attributes. By default true, optional.
• IncludeScopeProperties : If you're doing structured logging, this determines whether to include NLog ScopeContext properties as attributes. By default false, optional.
• IncludeEventParameters : Whether to fallback to including NLog LogEvent parameters as attributes, when no NLog LogEvent properties. By default false, optional.
• ResolveOptionsFromName : Allows you to use the Options pattern to initialize the target using an instance of OtlpExporterOptions defined in appsettings.json. If the setting is not empty, NLog will try to resolve OtlpExporterOptions from the name given by this setting and UseHttp, Endpoint and Headers will be ignored. For an example, see the TestWebApp project.
• ExcludeProperties : A list of log event properties which won't be added to the final log as attributes. By default empty, meaning that no log event properties will be excluded.
• OnlyIncludeProperties : A list of log event properties which will be the only ones to be included in the final log. If both this and ExcludeProperties are defined, this setting will take precedence and ExcludeProperties will be ignored.