[exporter/azuremonitor] Exporter doesn't export span links

[tombiddulph]

Component(s)

exporter/azuremonitor

What happened?

Description

The AzureMonitor exporter doesn't seem to export span links. I've had a look through the code and I can't see any mapping of span links taking place.

Steps to Reproduce

In a C# app with otel configured and pointing to a collector with the azure monitor exporter

var remoteActivity = GetActivityFromSomeRemoteSource();
var myActivity = CreateLocalActivityWithoutRemoteContext( links: new List<ActivityLink> { new ActivityLink(remoteActivity.Context} );

Expected Result

Link between activities to appear in application insights timeline view

Actual Result

No link in timeline view

Collector version

a2a52e43c1a80aa94120ad78c2db68780eb90e6d11c8db5b3ce2f6a0cc6b5029

Environment information

Environment

OS: (macos 14.7)
Collector image otel/opentelemetry-collector-contrib sha256:a2a52e43c1a80aa94120ad78c2db68780eb90e6d11c8db5b3ce2f6a0cc6b5029
Dotnet sdk: 8.0.401
OpenTelemetry.* Nuget packages: 1.9.0

OpenTelemetry Collector configuration

receivers:
  otlp:
    protocols:
      grpc:
        endpoint: 0.0.0.0:4317
      http:
        endpoint: 0.0.0.0:4318
    
processors:
exporters:
  debug:
    verbosity: detailed # '
  azuremonitor:
    connection_string: 
    spaneventsenabled: true

service:
  telemetry:
    logs:
      level: debug
  pipelines:
    traces:
      receivers: [otlp]
      processors: []
      exporters: [ debug, azuremonitor]
    logs:
      receivers: [otlp]
      processors: []
      exporters: [debug, azuremonitor]

Log output

2024-10-17 09:16:32 SpanLink #0
2024-10-17 09:16:32      -> Trace ID: 8a399a6101a2783da2ee92c57c6dc77f
2024-10-17 09:16:32      -> ID: ce21439755dcecfe
2024-10-17 09:16:32      -> TraceState: 
2024-10-17 09:16:32      -> DroppedAttributesCount: 0

Additional context

I've attached logs from the collector showing that span are being produced links

Workaround

Setting a tag on the localActivity with the key of _MS.links and and array of operation links with the following schema links the activities in the application insights timeline view

[
   {
       "operation_Id": <remoteActivity.Context.TraceId>,
       "id":  <remoteActivity.Context.SpanId>
   }
]

Processor

 public class LinkProcessor : BaseProcessor<Activity>
 {
        public override void OnEnd(Activity data)
        {
            if (data.Links.Any())
            {
                var links = data.Links.Select(activityLink => new OperationLink(activityLink.Context.TraceId.ToString(), activityLink.Context.SpanId.ToString())).ToList();
                data.SetTag("_MS.links", JsonSerializer.Serialize(links));
            }
            base.OnEnd(data);
        }

        private record OperationLink(
            [property: JsonPropertyName("operation_Id")] string OperationId,
            [property: JsonPropertyName("id")] string Id);
}

[github-actions]

Pinging code owners:

• exporter/azuremonitor: @pcwiese

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