This section explains a few concepts that you need to understand before you get started with tracing. In the context of this document, a service is synonymous with an application. A span is the basic unit of work done within a single service, on a single host. Every span has a name, starting timestamp, and duration. For example, the work done by a REST endpoint is a span. A span is associated to a single service, but its descendants can belong to different services and hosts. A trace contains a collection of spans from one or more services, running on one or more hosts. For example, if you trace a service endpoint that calls another service, then the trace would contain spans from both services. Within a trace, spans are organized as a directed acyclic graph (DAG) and can belong to multiple services, running on multiple hosts. The OpenTracing Data Model describes the details at The OpenTracing Semantic Specification. Spans are automatically created by Helidon as needed during execution of the REST request.

Use the Helidon MP Maven archetype to create a simple project that can be used for the examples in this guide.

mvn archetype:generate -DinteractiveMode=false \
    -DarchetypeGroupId=io.helidon.archetypes \
    -DarchetypeArtifactId=helidon-quickstart-mp \
    -DarchetypeVersion=1.4.12 \
    -DgroupId=io.helidon.examples \
    -DartifactId=helidon-quickstart-mp \
    -Dpackage=io.helidon.examples.quickstart.mp

cd helidon-quickstart-mp

First, you need to run the Zipkin tracer. Helidon will communicate with this tracer at runtime.

docker run -d --name zipkin -p 9411:9411 openzipkin/zipkin  

• Run the Zipkin docker image named openzipkin/zipkin.

curl http://localhost:9411/health 
...
{
  "status": "UP", 
  "zipkin": {
    "status": "UP",
    "details": {
      "InMemoryStorage{}": {
        "status": "UP"
      }
    }
  }
}

• Invoke the Zipkin REST API to check the Zipkin server health.
• All status fields should be UP.

Update the pom.xml file and add the following Zipkin dependency to the <dependencies> section (not <dependencyManagement>). This will enable Helidon to use Zipkin at the default host and port, localhost:9411.

<dependency>
  <groupId>io.helidon.tracing</groupId>
  <artifactId>helidon-tracing-zipkin</artifactId>
</dependency>

All spans sent by Helidon to Zipkin need to be associated with a service. Specify the service name below.

tracing.service=helidon-mp-1

mvn package -DskipTests=true
java -jar target/helidon-quickstart-mp.jar

curl http://localhost:8080/greet
...
{
  "message": "Hello World!"
}

Because you had tracing enabled, the previous /greet endpoint invocation resulted in a new trace being created. Let’s get the trace data that was generated using the Zipkin API. First, get the service information.

curl http://localhost:9411/api/v2/services
...
["helidon-mp-1"] 

• This is the tracing service name specified in META-INF/microprofile-config.properties.

Each span used by a service has a name, which is unique within a trace. If you invoke the /greet endpoint multiple times, you will still get the same set of names.

curl -X GET "http://localhost:9411/api/v2/spans?serviceName=helidon-mp-1" -H "accept: application/json"
...
[ 
  "content-read",
  "content-write",
  "get:io.helidon.examples.quickstart.mp.greetresource.getdefaultmessage",
  "security",
  "security:atn",
  "security:atz",
  "security:response"
]

• Get the span names for the helidon-mp-1 service.
• These are the span names. If you invoke the /greet endpoint again, then invoke the /spans endpoint, you will get the same response.

Next, get the contents of the trace as shown below. Notice that each span has a parentId field, except the get:io.helidon.examples.quickstart.mp.greetresource.getdefaultmessage span, which is the root.

curl -X GET "http://localhost:9411/api/v2/traces?serviceName=helidon-mp-1&limit=1" -H "accept: application/json"
...
[
  [ 
    {
      "traceId": "2e0af8866efdef35",
      "parentId": "2e0af8866efdef35",
      "id": "b5d61690f230fde4",
      "kind": "SERVER",
      "name": "content-read",
      "timestamp": 1568077339998659,
      "duration": 41,
      "localEndpoint": {
        "serviceName": "helidon-mp-1",
        "ipv4": "192.168.1.115"
      },
      "tags": {
        "requested.type": "java.io.InputStream"
      }
    },
...
(truncated)
]

• Get the newest trace only, using the limit=1 query param. There are other query params that let you restrict results to a specific time window.
• The request will return seven spans, one for each name, along with an unnamed JSON node, which has the status.

The tracing output data is verbose and can be difficult to interpret using the REST API, especially since it represents a structure of spans. Zipkin provides a web-based UI at http://localhost:9411/zipkin, where you can see a visual representation of the same data and the relationship between spans within a trace. If you see a Lens UI button at the top center then click on it and it will take you to the specific UI used by this guide.

Click on the UI refresh button (the search icon) as shown in the image below. Notice that you can change the look-back time to restrict the trace list.

The image below shows the trace summary, including start time and duration of each trace. There are two traces, each one generated in response to a curl http://localhost:8080/greet invocation. The oldest trace will have a much longer duration since there is one-time initialization that occurs.

Click on a trace and you will see the trace detail page where the spans are listed. You can clearly see the root span and the relationship among all the spans in the trace, along with timing information.

You can examine span details by clicking on the span row. Refer to the image below, which shows the security span details, including timing information. You can see times for each space relative to the root span. These rows are annotated with Server Start and Server Finish, as shown in the third column.

So far, you have used tracing with JAX-RS without needing to annotate. You can enable tracing on other CDI beans, either at the class level or at the method level, as shown by the following examples.

Tracing at the method level

To trace at the method level, you just annotate a method with @Traced.

Update the GreetingProvider class; 1) Add a new import and 2) Add the @Traced annotation to the getMessage method:

import org.eclipse.microprofile.opentracing.Traced; 
...
    @Traced  
    String getMessage() {
        return message.get();
    }
...

content_copy Copied

• Import the Traced annotation.
• Enable tracing for getMessage.

Build and run the application, then invoke the endpoints and check the response:

curl http://localhost:8080/greet
curl -X GET "http://localhost:9411/api/v2/spans?serviceName=helidon-mp-1" -H "accept: application/json"
...
[
  "content-read",
  "content-write",
  "dosomework",
  "get:io.helidon.examples.quickstart.mp.greetresource.getdefaultmessage",
  "io.helidon.examples.quickstart.mp.greetingprovider.getmessage", 
  "security",
  "security:atn",
  "security:atz",
  "security:response"
]

content_copy Copied

• There is new span name for the getmessage method, since your code called that method during the invocation of /greet.

Click the back button on your browser, then click on the UI refresh button to see the new trace. Select the newest trace in the list to see the trace detail page like the one below. Notice the new span named io.helidon.examples.quickstart.mp.greetingprovider.getmessage.

Trace detail page with new span getmessage

Tracing at the class level

@Traced 
@ApplicationScoped
public class GreetingProvider {
...

    String getMessage() { 
        return message.get();
    }

curl http://localhost:8080/greet
curl -X GET "http://localhost:9411/api/v2/spans?serviceName=helidon-mp-1" -H "accept: application/json"
[
...
  "io.helidon.examples.quickstart.mp.greetingprovider.getmessage", 
...
]

Invoke the endpoints and check the response:
----
curl -i -X PUT -H "Content-Type: application/json" -d '{"greeting": "Hi"}'  http://localhost:8080/greet/greeting 
curl -X GET "http://localhost:9411/api/v2/spans?serviceName=helidon-mp-1" -H "accept: application/json"
...
[
  "content-read",
  "content-write",
  "get:io.helidon.examples.quickstart.mp.greetresource.getdefaultmessage",
  "io.helidon.examples.quickstart.mp.greetingprovider.getmessage",
  "io.helidon.examples.quickstart.mp.greetingprovider.setmessage", 
  "put:io.helidon.examples.quickstart.mp.greetresource.updategreeting", 
  "security",
  "security:atn",
  "security:atz",
  "security:response"
]
----
<1> Invoke the endpoint to change the greeting.
<2> The `GreetingProvider.setmessage` method was traced since you enabled class level tracing.
<3> The JAX-RS method `GreetResource.updategreeting` was traced automatically by Helidon.

@ApplicationScoped
public class GreetingProvider {
    private final AtomicReference<String> message = new AtomicReference<>();

    @Inject
    public GreetingProvider(@ConfigProperty(name = "app.greeting") String message) {
        this.message.set(message);
    }

    @Traced 
    String getMessage() {
        return getMessage2();
    }

    @Traced  
    String getMessage2() {
        return message.get();
    }

    void setMessage(String message) {
        this.message.set(message);
    }
}

curl http://localhost:8080/greet
curl -X GET "http://localhost:9411/api/v2/spans?serviceName=helidon-mp-1" -H "accept: application/json"
...
[
...
  "io.helidon.examples.quickstart.mp.greetingprovider.getmessage", 
...
]

Helidon automatically traces across services, providing that the services use the same tracer, for example, the same instance of Zipkin. This means a single trace can include spans from multiple services and hosts. OpenTracing uses a SpanContext to propagate tracing information across process boundaries. When you make client API calls, Helidon will internally call OpenTracing APIs to propagate the SpanContext. There is nothing you need to do in your application to make this work.

To demonstrate distributed tracing, you will need to create a second project, where the server listens on port 8081. Create a new root directory to hold this new project, then do the following steps, similar to what you did at the start of this guide:

Create a second service

mvn archetype:generate -DinteractiveMode=false \
    -DarchetypeGroupId=io.helidon.archetypes \
    -DarchetypeArtifactId=helidon-quickstart-mp \
    -DarchetypeVersion=1.4.12 \
    -DgroupId=io.helidon.examples \
    -DartifactId=helidon-quickstart-mp-2 \
    -Dpackage=io.helidon.examples.quickstart.mp

cd helidon-quickstart-mp-2

<dependency>
  <groupId>io.helidon.tracing</groupId>
  <artifactId>helidon-tracing-zipkin</artifactId>
</dependency>

app.greeting=Hello From MP-2
tracing.service=helidon-mp-2

# Microprofile server properties
server.port=8081
server.host=0.0.0.0

mvn package -DskipTests=true
java -jar target/helidon-quickstart-mp-2.jar

curl http://localhost:8081/greet
...
{
  "message": "Hello From MP-2 World!"
}

Modify the first service

Once you have validated that the second service is running correctly, you need to modify the original application to call it.

Replace the GreetResource class with the following code:

package io.helidon.examples.quickstart.mp;

import java.util.Collections;
import javax.enterprise.context.RequestScoped;
import javax.inject.Inject;
import javax.json.Json;
import javax.json.JsonBuilderFactory;
import javax.json.JsonObject;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.client.WebTarget;
import javax.ws.rs.core.MediaType;
import org.glassfish.jersey.server.Uri;

@Path("/greet")
@RequestScoped
public class GreetResource {

  @Uri("http://localhost:8081/greet")
  private WebTarget target; 

  private static final JsonBuilderFactory JSON = Json.createBuilderFactory(Collections.emptyMap());
  private final GreetingProvider greetingProvider;

  @Inject
  public GreetResource(GreetingProvider greetingConfig) {
    this.greetingProvider = greetingConfig;
  }

  @SuppressWarnings("checkstyle:designforextension")
  @GET
  @Produces(MediaType.APPLICATION_JSON)
  public JsonObject getDefaultMessage() {
    return createResponse("World");
  }

  @GET
  @Path("/outbound") 
  public JsonObject outbound() {
    return target.request().accept(MediaType.APPLICATION_JSON_TYPE).get(JsonObject.class);
  }

  private JsonObject createResponse(String who) {
    String msg = String.format("%s %s!", greetingProvider.getMessage(), who);

    return JSON.createObjectBuilder().add("message", msg).build();
  }
}

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• This is the WebTarget needed to send a request to the second service at port 8081.
• This is the new endpoint that will call the second service.

Build and run the application, then invoke the endpoint and check the response:

curl -i http://localhost:8080/greet/outbound 
...
{
  "message": "Hello From MP-2 World!" 
}

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• The request went to the service on 8080, which then invoked the service at 8081 to get the greeting.
• Notice the greeting came from the second service.

Refresh the Zipkin UI trace listing page and notice that there is a trace across two services.

Tracing multiple service list view

Click on the trace with two services to see the detail view.

Tracing across multiple services detail view

In the image above, you can see that the trace includes spans from two services. You will notice there is a gap before the sixth span, which is a get operation. This is a one-time client initialization delay. Run the /outbound curl command again and look at the new trace to see that the delay no longer exists.

You can now stop your second service, it is no longer used in this guide.

apiVersion: v1
kind: Service
metadata:
  name: zipkin
spec:
  ports:
    - port: 9411
      protocol: TCP
  selector:
    app: zipkin
---
kind: Pod
apiVersion: v1
metadata:
  name: zipkin
  labels:
    app: zipkin
spec:
  containers:
    - name: zipkin
      image: openzipkin/zipkin
      imagePullPolicy: IfNotPresent
      ports:
        - containerPort: 9411

kubectl apply -f ./zipkin.yaml

kubectl expose pod  zipkin --name=zipkin-external --port=9412 --target-port=9411 --type=LoadBalancer 

• Create a service so that you can access the Zipkin UI.

Navigate to http://localhost:9412/zipkin to validate that you can access Zipkin running in Kubernetes. It may take a few seconds before it is ready.

kind: Service
apiVersion: v1
metadata:
  name: helidon-tracing 
  labels:
    app: helidon-tracing
spec:
  type: NodePort
  selector:
    app: helidon-tracing
  ports:
    - port: 8080
      targetPort: 8080
      name: http
---
kind: Deployment
apiVersion: extensions/v1beta1
metadata:
  name: helidon-tracing
spec:
  replicas: 1 
  template:
    metadata:
      labels:
        app: helidon-tracing
        version: v1
    spec:
      containers:
        - name: helidon-tracing
          image: helidon-tracing-mp
          imagePullPolicy: IfNotPresent
          ports:
            - containerPort: 8080

• A service of type NodePort that serves the default routes on port 8080.
• A deployment with one replica of a pod.

kubectl apply -f ./tracing.yaml

kubectl get service/helidon-tracing

NAME             TYPE       CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
helidon-tracing   NodePort   10.99.159.2   <none>        8080:31143/TCP   8s 

• A service of type NodePort that serves the default routes on port 31143.

curl http://localhost:31143/greet
...
{
  "message": "Hello World!"
}

Access the Zipkin UI at http://localhost:9412/zipkin and click on the refresh icon to see the trace that was just created.

You can now delete the Kubernetes resources that were just created during this example.

kubectl delete -f ./zipkin.yaml
kubectl delete -f ./tracing.yaml
kubectl delete service zipkin-external
docker rm -f zipkin