[GitHub] [incubator-zipkin] tmichnik1981 opened a new issue #2616: Not all client to client relations taken into account in 'Dependencies' tree

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tmichnik1981 opened a new issue #2616: Not all client to client relations taken into account in 'Dependencies' tree 
URL: https://github.com/apache/incubator-zipkin/issues/2616
 
 
   ## Describe the Bug
   
   zipkin: 2.12.9
   
   Some relations between  client services are not visible  on the graph.
   
   ## Steps to Reproduce
   
   We came across two problems when analyzing dependencies.
   
   The first one,  when component A (within service 1) calls component B  (still within service 1)  and then  component B  calls component C in service 2.
   It turned out that only relation B --> C is visible.
   
   I found in **zipkin2.internal.DependencyLinker** a condition causing this problem:
   **line: 70**
   
   ```
   // When processing links to a client span, we prefer the server's name. If we have no child
   // spans, we proceed to use the name the client chose.
   if (Kind.CLIENT.equals(kind) && !current.children().isEmpty()) {
      continue;
   }
   ```
   
   It looks like it's done on purpose but I do not understand why. 
   Why do we want to  skip CLIENT spans which might possess some children?
   
   When I commented out that suspicious condition, the dependency graph was almost correct.
   
   I am saying "almost" because I spotted another thing.
   
   When CLIENT span A calls CLIENT span B and they have the same service name, the link is not built. IMHO it might be visible on the graph  as a node with a link to itself.
   
   I found in **zipkin2.internal.DependencyLinker** there is code probably preventing this kind of relations: 
   **line 127**
   ```
    if (kind == Kind.CLIENT && serviceName != null && !remoteAncestorName.equals(serviceName)) {
   ///.......//
   }
   ```
   
   [zipkin-sample-spans.txt](https://github.com/apache/incubator-zipkin/files/3223851/zipkin-sample-spans.txt)
   
   
   
   ## Expected Behaviour
   
   The dependency diagram including all relations.
   
   

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