opentelemetry-dotnet/docs/logs/extending-the-sdk

Extending the OpenTelemetry .NET SDK

• Building your own exporter
• Building your own processor
• Building your own sampler
• References

Exporter

OpenTelemetry .NET SDK has provided the following built-in log exporters:

• InMemory
• Console
• OpenTelemetryProtocol

Custom exporters can be implemented to send telemetry data to places which are not covered by the built-in exporters:

• Exporters should derive from OpenTelemetry.BaseExporter<LogRecord> (which belongs to the OpenTelemetry package) and implement the Export method.
• Exporters can optionally implement the OnForceFlush and OnShutdown method.
• Depending on user's choice and load on the application, Export may get called with one or more log records.
• Exporters should not throw exceptions from Export, OnForceFlush and OnShutdown.
• Exporters should not modify log records they receive (the same log records may be exported again by different exporter).
• Exporters are responsible for any retry logic needed by the scenario. The SDK does not implement any retry logic.
• Exporters should avoid generating telemetry and causing live-loop, this can be done via OpenTelemetry.SuppressInstrumentationScope.

class MyExporter : BaseExporter<LogRecord>
{
    public override ExportResult Export(in Batch<LogRecord> batch)
    {
        using var scope = SuppressInstrumentationScope.Begin();

        foreach (var record in batch)
        {
            Console.WriteLine($"Export: {record}");
        }

        return ExportResult.Success;
    }
}

A demo exporter which simply writes log records to the console is shown here.

Apart from the exporter itself, you should also provide extension methods as shown here. This allows users to add the Exporter to the OpenTelemetryLoggerOptions as shown in the example here.

Processor

OpenTelemetry .NET SDK has provided the following built-in processors:

• BatchExportProcessor<T>
• CompositeProcessor<T>
• SimpleExportProcessor<T>

Custom processors can be implemented to cover more scenarios:

• Processors should inherit from OpenTelemetry.BaseProcessor<LogRecord> (which belongs to the OpenTelemetry package), and implement the OnEnd method.
• Processors can optionally implement the OnForceFlush and OnShutdown methods. OnForceFlush should be thread safe.
• Processors should not throw exceptions from OnEnd, OnForceFlush and OnShutdown.
• OnEnd should be thread safe, and should not block or take long time, since they will be called on critical code path.

class MyProcessor : BaseProcessor<LogRecord>
{
    public override void OnEnd(LogRecord record)
    {
        Console.WriteLine($"OnEnd: {record}");
    }
}

A demo processor is shown here.

Sampler

TBD

References