
[id='tracing-a-complex-service_{context}']
= Tracing a complex service

In this example, you can see how to trace a more complex service that performs an external service invocation.
To keep the example easy to use, the application actually calls itself, but in a way that is equivalent to calling services outside of the application.

In this example, Jaeger runs locally using Docker.

.Prerequisites

* A xref:tracing-a-single-service_{context}[simple service tracing] configured.

.Procedure

. If the Jaeger tracer is running, restart it:
.. Open the console where the container with Jaeger is running and stop it by pressing `Ctrl + C`.
.. Relaunch the container by running:
+
[source,bash]
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# docker run -it --rm -p 6831:6831/udp -p 16686:16686 jaegertracing/all-in-one
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. Use JAX-RS Client to invoke an external service, for example:
+
--
.MyComplexResource.java
[source,java]
----
include::src/main/java/org/wildfly/swarm/howto/tracing/MyComplexResource.java[tag=complex-resource,indent=0]
----

.MyService.java
[source,java]
----
include::src/main/java/org/wildfly/swarm/howto/tracing/MyService.java[tag=traced-service-method,indent=0]
----

Here, you can see that not only JAX-RS resource methods can be traced.
This is a regular method in a CDI bean.
Unlike JAX-RS resources, which are traced automatically, other methods need the explicit `@Traced` annotation.

The most important part is this usage of MicroProfile OpenTracing API:

[source,java]
----
include::src/main/java/org/wildfly/swarm/howto/tracing/MyService.java[tag=client-registration,indent=0]
----

This snippet shows how MicroProfile OpenTracing integrates with JAX-RS Client to ensure the trace is propagated across services.
Without the integration, it would be impossible to correlate the invocations as part of a single user request.

[NOTE]
====
Currently, MicroProfile OpenTracing does not integrate with MicroProfile RestClient, so you need to use a pure JAX-RS Client.
This limitation will be removed in the future, see link:https://github.com/eclipse/microprofile-opentracing/issues/82[MicroProfile OpenTracing issue #82^].
====
--

. Launch your application:
+
[source,bash,opts="nowrap"]
----
$ mvn thorntail:run
----

. Invoke the traced endpoint several times:
+
--
[source,bash]
----
$ curl http://localhost:8080/complex
Called an external service successfully, it responded: Hello from traced endpoint
----

Notice how the _complex_ service calls the _simple_ service, which you configured in the simple service example.
Both of these services are traced, so we can see the invocation of the _simple_ service as a part of the _complex_ invocation.
--

. See the traces in Jaeger UI.
+
--
Reload the Jaeger UI at link:http://localhost:16686/[http://localhost:16686/^], select `greeter` under _Service_ and click _Find Traces_.
You can see all the requests you performed and basic information about them.

Click on one of the traces to show detailed information about that particular request:

* At the top level, you can see the JAX-RS resource method `MyComplexResource.get`.
* Under it, you can see the invocation of `MyService.call` method.
* Under that, you can see that this method performed a `GET` request to another service.
* Under the `GET` request, you can see the JAX-RS resource method `MySimpleResource.get`.

For all these invocations, you can see how long they took and when they occurred as part of the entire request processing.
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