How to Create OpenTelemetry Spans from a String TraceID in a Distributed System?

Creating OpenTelemetry Spans from a String TraceID

When dealing with distributed systems, it's crucial to maintain context and trace relationships across components. In this case, where the publisher uses message headers to propagate trace information, we can still construct OpenTelemetry spans on the subscriber side using the received traceID string.

Constructing the SpanContext from Header Values

To create a span with its parents correctly linked, we need to convert the traceID and spanID strings extracted from the request headers into trace.TraceID and trace.SpanID objects. We achieve this using the following functions:

<code class="go">var traceID trace.TraceID
traceID, err = trace.TraceIDFromHex(request.TraceID)
var spanID trace.SpanID
spanID, err = trace.SpanIDFromHex(request.SpanID)</code>

With the traceID and spanID objects, we can construct a SpanContext. We need to set the Remote flag to false, indicating that this span is not being exported to a remote system:

<code class="go">var spanContextConfig trace.SpanContextConfig
spanContextConfig.TraceID = traceID
spanContextConfig.SpanID = spanID
spanContextConfig.TraceFlags = 01
spanContextConfig.Remote = false
spanContext = trace.NewSpanContext(spanContextConfig)</code>

Creating a New Span with the SpanContext

To create a new span with this constructed SpanContext, we first need to enrich a new context with it:

<code class="go">requestContext := context.Background()
requestContext = trace.ContextWithSpanContext(requestContext, spanContext)</code>

Then, we can start a new child span using the enriched context:

<code class="go">var requestInLoopSpan trace.Span
childContext, requestInLoopSpan := otel.Tracer("inboundmessage").Start(requestContext, "requestInLoopSpan")</code>

This child span will be linked to the parent span on the publisher side, allowing for proper context propagation throughout the distributed system.

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