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Link

A link describes a cross-relationship between spans in either the same or different trace. For example if a batch operation were performed, comprising of different traces or different processes, a link from one span to another can help correlate related spans.

Constituents

It consists of fields:

Uses and advisory

Please also take a look at specs/utils.HandlingUntrustedRequests

Source code samples

In these source code samples, we have two spans:

Name Description
SpanA Started from an untrusted boundary e.g. a client request to your cloud
SpanB Started from a trusted boundary e.g. from the frontend server of your service/cloud
// SpanA started say on the client side
_, spanA := trace.StartSpan(context.Background(), "SpanA")
spanASC := spanA.SpanContext()

_, spanB := trace.StartSpan(context.Background(), "SpanB")
spanB.AddLink(trace.Link{
        TraceID: spanASC.TraceID,
        SpanID:  spanASC.SpanID,
        Type:    trace.LinkTypeChild,
        Attributes: map[string]interface{}{
                "reason": "client-RPC unverified source",
        },
})
// SpanA started say on the client side
// SpanB started on the server side
Scope s1 = tracer.spanBuilder("SpanA").startScopedSpan();
SpanContext spanASC = tracer.getCurrentSpan().getContext();
s1.close();

Scope s2 = tracer.spanBuilder("SpanB").startScopedSpan();
Map<String, AttributeValue> linkAttributes = new HashMap<>();
linkAttributes.put("reason", AttributeValue.stringAttribute("client-RPC unverified source"));
tracer.getCurrentSpan().addLink(
  Link.fromSpanContext(spanASC, Link.Type.CHILD_LINKED_SPAN, linkAttributes));
s2.close();
# SpanA started say on the client side
# SpanB started on the server side
spanA = tracer.start_span(name='SpanA')
tracer.end_span()

spanB = tracer.start_span(name='SpanB')
linkAttributes = attributes.Attributes(reason="client-RPC unverified source")
spanB.add_link(Link(
  trace_id=spanA.context_tracer.trace_id,
  span_id=spanA.span_id,
  attributes=linkAttributes
))
tracer.end_span()
let spanATraceId;
let spanASpanId;

// SpanA started say on the client side
tracer.startRootSpan({name: 'SpanA', samplingRate: 1.0}, spanA => {
  spanATraceId = spanA.traceId;
  spanASpanId = spanA.id;
  // Do something with spanA
  spanA.end();
});

// SpanB started on the server side
tracer.startRootSpan({name: 'SpanB', samplingRate: 1.0}, spanB => {
  linkAttributes = {'reason': 'client-RPC unverified source'};
  spanB.addLink(spanATraceId, spanASpanId, linkAttributes);
  // Do something with spanB
  spanB.end()
});

Visuals

When examined after being exported

References

Resource URL
Handling untrusted requests specs/utils.HandlingUntrustedRequests
Data model proto/trace/v1.Link
Go API reference Span.AddLink and Link
Java API reference Span.addLink and Link
Python API reference Span.add_link and Link
Node.js API reference Span.addLink and Link