title: Spring Boot Jaeger create new Span for given TraceId
body: <p>so I'm playing aroung with Jaeger and OpenTracing to trace the requests between my Spring Boot microservices. I have setup all necessary configurations and added the dependency:</p>
  
  <pre><code>&lt;dependency&gt;
      &lt;groupId&gt;io.opentracing.contrib&lt;/groupId&gt;
      &lt;artifactId&gt;opentracing-spring-jaeger-web-starter&lt;/artifactId&gt;
      &lt;version&gt;2.0.3&lt;/version&gt;
  &lt;/dependency&gt;
  </code></pre>
  
  <p>So far all works fine. I see all the traces and spans in my Jaeger UI, no problem. </p>
  
  <p>But now I have the challenge to add new spans to a specific trace, that is already finished. Think of it like this. A client calls one of the services and the tracing starts. After the work is done, I see the trace in my Jaeger UI. But now the invoking clients wants to add some additional tracing data to the specific trace. Like tracing information from other service, that are not within the scope of my microservices. I've added a filter so I can extract the trace id and send it to the client. Now the client does a request containing the additional trace information and the trace id. These informationa should then be added as an additional span in the already finished trace.</p>
  
  <p>Now to my question. Is there a way to create a span and add it to a trace with only having the trace id as a String? </p>
  
  <p>I've tried Zipkin and I could just do:</p>
  
  <pre><code>Span span = new SpanBuilder()
                  .name(someName)
                  .traceId(traceId)
                  .parentId(traceId)
                  .id(someId)
                  .kind(Kind.CLIENT)
                  .build()
  </code></pre>
  
  <p>That span could then be added by doing a POST request to my zipkin server on port 9411 which did the magic of adding this span to the trace with the given id.</p>
  
  <p>Using OpenTracing I can do:</p>
  
  <pre><code>Span span = tracer.buildSpan(someName)
                  .asChildOf(**traceSpan**)
                  .withStartTimestamp(someTime)
                  .ignoreActiveSpan()
                  .start();
  </code></pre>
  
  <p>Unfortunately this approach needs the trace in form of a span to create the new span as a child of that trace. Given the fact that I can only provide the trace id, I don't know how to get the needed span of that trace. Do I really need to make a call to my the Jaeger query to get the trace span needed or is there another approach I haven't been thinking of?</p>
  
  <p>Would really like to get some help on this. </p>
  
  <p>Cheers!</p>