Tracing

This guide describes how to create a sample MicroProfile (MP) project that can be used to run some basic examples using tracing with Helidon MP.

What You Need

For this 30 minute tutorial, you will need the following:

Prerequisite product versions for Helidon 4.4.0-SNAPSHOT

Verify Prerequisites:

java -version
mvn --version
docker --version
kubectl version

Setting JAVA_HOME:

# On Mac
export JAVA_HOME=`/usr/libexec/java_home -v 21`

# On Linux
# Use the appropriate path to your JDK
export JAVA_HOME=/usr/lib/jvm/jdk-21

Introduction

Distributed tracing is a critical feature of microservice based applications, since it traces workflow both within a service and across multiple services. This provides insight to sequence and timing data for specific blocks of work, which helps you identify performance and operational issues. Helidon MP includes support for distributed tracing through the OpenTracing API. Tracing is integrated with WebServer and Security using either the Zipkin or Jaeger tracers.

Tracing Concepts

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.

Getting Started with Tracing

The examples in this guide demonstrate how to integrate tracing with Helidon, how to view traces, how to trace across multiple services, and how to integrate tracing with Kubernetes. All examples use Jaeger and traces will be viewed using Jaeger UI.

Create a Sample Helidon MP project

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

Run the Maven archetype:

mvn -U archetype:generate -DinteractiveMode=false \
    -DarchetypeGroupId=io.helidon.archetypes \
    -DarchetypeArtifactId=helidon-quickstart-mp \
    -DarchetypeVersion=4.4.0-SNAPSHOT \
    -DgroupId=io.helidon.examples \
    -DartifactId=helidon-quickstart-mp \
    -Dpackage=io.helidon.examples.quickstart.mp

The project will be built and run from the helidon-quickstart-mp directory:

cd helidon-quickstart-mp

Set up Jaeger

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

Run Jaeger within a docker container, then check the Jaeger server working:

docker run -d --name jaeger \                  <1>
  -e COLLECTOR_OTLP_ENABLED=true \
  -p 6831:6831/udp \
  -p 6832:6832/udp \
  -p 5778:5778 \
  -p 16686:16686 \
  -p 4317:4317 \
  -p 4318:4318 \
  -p 14250:14250 \
  -p 14268:14268 \
  -p 14269:14269 \
  -p 9411:9411 \
  jaegertracing/all-in-one:1.50

Check the Jaeger server by opening in browser:

http://localhost:16686/search

Enable Tracing in the Helidon Application

Update the pom.xml file and add the following Jaeger dependency to the <dependencies> section (not <dependencyManagement>). This will enable Helidon to use Jaeger at the default host and port, localhost:14250.

Add the following dependency to pom.xml:

<dependencies>
  <dependency>
    <groupId>io.helidon.microprofile.tracing</groupId>
    <artifactId>helidon-microprofile-tracing</artifactId>
  </dependency>
  <dependency>
    <groupId>io.helidon.tracing.providers</groupId>
    <artifactId>helidon-tracing-providers-jaeger</artifactId>
  </dependency>
</dependencies>

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

Add the following line to META-INF/microprofile-config.properties:

tracing.service=helidon-mp-1

Build the application, skipping unit tests, then run it:

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

Run the curl command in a new terminal window and check the response:

curl http://localhost:8080/greet

{
  "message": "Hello World!"
}

View Tracing Using Jaeger UI

The tracing output data is verbose and can be difficult to interpret using the REST API, especially since it represents a structure of spans. Jaeger provides a web-based UI at http://localhost:16686/search, 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 Find traces button (the search icon) as shown in the image below.

Jaeger UI

The image below shows the trace summary, including start time and duration of each trace. There are several 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.

Tracing list view

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.

Trace detail page

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.

Enable Tracing on CDI Beans

So far in this tutorial, 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.

Add the @Traced annotation to the getMessage method:

class GreetingProvider {
    @Traced1
    String getMessage() {
        return message.get();
    }
}

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

curl http://localhost:8080/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.

Tracing at the Class Level

To trace at the class level, annotate the class with @Traced. This will enable tracing for all class methods, except for the constructor and private methods.

Add @Traced to the GreetingProvider class and remove @Traced from the getMessage method:

@Traced1
@ApplicationScoped
public class GreetingProvider {

    String getMessage() {2
        return message.get();
    }
}

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

curl http://localhost:8080/greet

You can refresh the UI view and drill down the trace to see the new spans.

Update the GreetingProvider class with the following code:

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

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

    @Traced1
    String getMessage() {
        return getMessage2();
    }

    @Traced2
    String getMessage2() {
        return message.get();
    }

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

Build and run the application, then invoke the endpoints:

curl http://localhost:8080/greet

Then check the response in the Jaeger UI in the browser.

Trace Across Services

Helidon automatically traces across services as long as the services use the same tracer, for example, the same instance of Jaeger. 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

Run the Maven archetype:

mvn -U archetype:generate -DinteractiveMode=false \
    -DarchetypeGroupId=io.helidon.archetypes \
    -DarchetypeArtifactId=helidon-quickstart-mp \
    -DarchetypeVersion=4.4.0-SNAPSHOT \
    -DgroupId=io.helidon.examples \
    -DartifactId=helidon-quickstart-mp-2 \
    -Dpackage=io.helidon.examples.quickstart.mp

The project will be built and run from the helidon-quickstart-mp directory:

cd helidon-quickstart-mp-2

Add the following dependency to pom.xml:

<dependency>
  <groupId>io.helidon.tracing.providers</groupId>
  <artifactId>helidon-tracing-providers-jaeger</artifactId>
</dependency>

Replace META-INF/microprofile-config.properties with the following:

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

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

Build the application, skipping unit tests, then run it:

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

Run the curl command in a new terminal window and check the response (notice the port is 8081):

curl http://localhost:8081/greet

{
  "message": "Hello From MP-2 World!"1
}

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:

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

    @Uri("http://localhost:8081/greet")
    private WebTarget target;1

    private static final JsonBuilderFactory JSON = Json.createBuilderFactory(Map.of());
    private final GreetingProvider greetingProvider;

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

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

    @GET
    @Path("/outbound")2
    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();
    }
}

curl -i http://localhost:8080/greet/outbound1

{
  "message": "Hello From MP-2 World!"1
}

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

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.

Integration with Kubernetes

The following example demonstrate how to use Jaeger from a Helidon application running in Kubernetes.

Add the following line to META-INF/microprofile-config.properties:

tracing.host=jaeger

Stop the application and build the docker image for your application:

docker build -t helidon-tracing-mp .

Deploy Jaeger into Kubernetes

Create the Kubernetes YAML specification, named jaeger.yaml, with the following contents:

apiVersion: v1
kind: Service
metadata:
  name: jaeger
spec:
  ports:
    - port: 16686
      protocol: TCP
  selector:
    app: jaeger
---
kind: Pod
apiVersion: v1
metadata:
  name: jaeger
  labels:
    app: jaeger
spec:
  containers:
    - name: jaeger
      image: jaegertracing/all-in-one
      imagePullPolicy: IfNotPresent
      ports:
        - containerPort: 16686

Create the Jaeger pod and ClusterIP service:

kubectl apply -f ./jaeger.yaml

Create a Jaeger external server and expose it on port 9142:

kubectl expose pod jaeger --name=jaeger-external --port=16687 --target-port=16686 --type=LoadBalancer1

Navigate to http://localhost:16687/search to validate that you can access Jaeger running in Kubernetes. It may take a few seconds before it is ready.

Deploy Your Helidon Application into Kubernetes

Create the Kubernetes YAML specification, named tracing.yaml, with the following contents:

kind: Service
apiVersion: v1
metadata:
  name: helidon-tracing1
  labels:
    app: helidon-tracing
spec:
  type: NodePort
  selector:
    app: helidon-tracing
  ports:
    - port: 8080
      targetPort: 8080
      name: http
---
kind: Deployment
apiVersion: apps/v1
metadata:
  name: helidon-tracing
spec:
  replicas: 12
  selector:
    matchLabels:
      app: helidon-tracing
  template:
    metadata:
      labels:
        app: helidon-tracing
        version: v1
    spec:
      containers:
        - name: helidon-tracing
          image: helidon-tracing-mp
          imagePullPolicy: IfNotPresent
          ports:
            - containerPort: 8080

Create and deploy the application into Kubernetes:

kubectl apply -f ./tracing.yaml

Access Your Application and the Jaeger Trace

Get the application service information:

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   8s1

Verify the tracing endpoint using port 31143, your port will likely be different:

curl http://localhost:31143/greet

{
  "message": "Hello World!"
}

Access the Jaeger UI at http://localhost:16687/search and click on the refresh icon to see the trace that was just created.

Cleanup

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

Delete the Kubernetes resources:

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

Responding to Span Lifecycle Events

Applications and libraries can register listeners to be notified at several moments during the lifecycle of every Helidon span:

• Before a new span starts
• After a new span has started
• After a span ends
• After a span is activated (creating a new scope)
• After a scope is closed

The next sections explain how you can write and add a listener and what it can do. See the SpanListener Javadoc for more information.

Understanding What Listeners Do

A listener cannot affect the lifecycle of a span or scope it is notified about, but it can add tags and events and update the baggage associated with a span. Often a listener does additional work that does not change the span or scope such as logging a message.

When Helidon invokes the listener’s methods it passes proxies for the Span.Builder, Span, and Scope arguments. These proxies limit the access the listener has to the span builder, span, or scope, as summarized in the following table. If a listener method tries to invoke a forbidden operation, the proxy throws a SpanListener.ForbiddenOperationException and Helidon then logs a WARNING message describing the invalid operation invocation.

Summary of Permitted Operations on Proxies Passed to Listeners

The following tables list specifically what operations the proxies permit.

io.helidon.tracing.Span.Builder Operations

io.helidon.tracing.Span Operations

io.helidon.tracing.Scope Operations

io.helidon.tracing.SpanContext Operations

Adding a Listener

Explicitly Registering a Listener on a Tracer

Create a SpanListener instance and invoke the Tracer#register(SpanListener) method to make the listener known to that tracer.

Automatically Registering a Listener on all Tracer Instances

Helidon also uses Java service loading to locate listeners and register them automatically on all Tracer objects. Follow these steps to add a listener service provider.

1. Implement the SpanListener interface.
2. Declare your implementation as a service provider:
   1. Create the file META-INF/services/io.helidon.tracing.SpanListener containing a line with the fully-qualified name of your class which implements SpanListener.
   2. If your service has a module-info.java file add the following line to it:

      provides io.helidon.tracing.SpanListener with <your-implementation-class>;
      

The SpanListener interface declares default no-op implementations for all the methods, so your listener can implement only the methods it needs to.

Helidon invokes each listener’s methods in the following order:

Order in which Helidon Invokes Listener Methods

Summary

This guide has demonstrated how to use the Helidon MP tracing feature with Jaeger. You have learned to do the following:

• Enable tracing within a service
• Use tracing with JAX-RS and CDI beans
• Use the Jaeger UI
• Use tracing across multiple services
• Integrate tracing with Kubernetes

Refer to the following references for additional information:

• MicroProfile OpenTracing specification
• MicroProfile OpenTracing Javadoc
• Helidon Javadoc