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= Helidon MP Tracing Guide
:description: Helidon tracing
:keywords: helidon, tracing, microprofile, guide
:toc:

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

[width=50%,role="flex, sm7"]
|===
|About 30 minutes
|<<about/03_prerequisites.adoc,Helidon Prerequisites>>
|===

== Introduction

Distributed tracing is a critical feature of micro-service 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 https://opentracing.io[OpenTracing API].  Tracing is integrated with WebServer, gRPC Server,
and Security using either the https://zipkin.io[Zipkin] or https://www.jaegertracing.io[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 https://opentracing.io/specification[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 with tracing with Kubernetes.  All examples use Zipkin and traces
will be viewed using both the Zipkin API and 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.

[source,bash,subs="attributes+"]
.Run the Maven archetype:
----
mvn archetype:generate -DinteractiveMode=false \
    -DarchetypeGroupId=io.helidon.archetypes \
    -DarchetypeArtifactId=helidon-quickstart-mp \
    -DarchetypeVersion={helidon-version} \
    -DgroupId=io.helidon.examples \
    -DartifactId=helidon-quickstart-mp \
    -Dpackage=io.helidon.examples.quickstart.mp
----

[source,bash]
.The project will be built and run from the `helidon-quickstart-mp` directory:
----
cd helidon-quickstart-mp
----

=== Setup Zipkin

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

[source,bash]
.Run Zipkin within a docker container, then check the Zipkin server health:
----
docker run -d --name zipkin -p 9411:9411 openzipkin/zipkin  // <1>
----
<1> Run the Zipkin docker image named `openzipkin/zipkin`.


[source,bash]
.Check the Zipkin server health:
----
curl http://localhost:9411/health // <1>
...
{
  "status": "UP", <2>
  "zipkin": {
    "status": "UP",
    "details": {
      "InMemoryStorage{}": {
        "status": "UP"
      }
    }
  }
}
----
<1> Invoke the Zipkin REST API to check the Zipkin server health.
<2> All `status` fields should be `UP`.

=== Enable Tracing in your Helidon application

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`.

[source,xml]
.Add the following dependency to `pom.xml`:
----
<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.

[source,bash]
.Add the following line to `META-INF/microprofile-config.properties`:
----
tracing.service=helidon-mp-1
----

[source,bash]
.Build the application, skipping unit tests, then run it:
----
mvn package -DskipTests=true
java -jar target/helidon-quickstart-mp.jar
----

[source,bash]
.Run the curl command in a new terminal window and check the response:
----
curl http://localhost:8080/greet
...
{
  "message": "Hello World!"
}
----


=== Viewing tracing using Zipkin REST API

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.

NOTE: Helidon automatically enables tracing for JAX-RS resources methods so you don't need to use annotations with JAX-RS.
See https://github.com/eclipse/microprofile-opentracing/releases/tag/1.3[MicroProfile OpenTracing] for more details.

[source,bash]
.Run the curl command and check the response:
----
curl http://localhost:9411/api/v2/services
...
["helidon-mp-1"] // <1>
----
<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.

[source,bash]
.Invoke the endpoint below and check the response:
----
// <1>
curl -X GET "http://localhost:9411/api/v2/spans?serviceName=helidon-mp-1" -H "accept: application/json"
...
[ // <2>
  "content-read",
  "content-write",
  "get:io.helidon.examples.quickstart.mp.greetresource.getdefaultmessage",
  "security",
  "security:atn",
  "security:atz",
  "security:response"
]
----
<1> Get the span names for the `helidon-mp-1` service.
<2> 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.

[source,bash]
.Invoke the endpoint below and check the response:
----
// <1>
curl -X GET "http://localhost:9411/api/v2/traces?serviceName=helidon-mp-1&limit=1" -H "accept: application/json"
...
[
  [ // <2>
    {
      "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)
]

----
<1> 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.
<2> The request will return seven spans, one for each name, along with an unnamed JSON node, which
has the status.

=== Viewing tracing using Zipkin 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.  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.

.Trace refresh
image::guides/12_tracing_refresh.png[Trace Refresh]


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.

.Tracing list view
image::guides/12_tracing_top.png[Traces]

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
image::guides/12_tracing_detail.png[Trace Detail]

NOTE: A parent span might not depend on the result of the child. This is called a `FollowsFrom` reference, see
https://github.com/opentracing/specification/blob/master/specification.md[Open Tracing Semantic Spec].  Notice, the
last span which writes the response after the root span ends, falls into this category.

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.

.Span detail page
image::guides/12_tracing_span_detail.png[Span Details]


=== Enabling Tracing on CDI beans

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.

[source,java]
.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; // <1>
...
    @Traced  // <2>
    String getMessage() {
        return message.get();
    }
...
----
<1> Import the `Traced` annotation.
<1> Enable tracing for getMessage.

[source,bash]
.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", // <1>
  "security",
  "security:atn",
  "security:atz",
  "security:response"
]
----
<1> 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`
image::guides/12_tracing_getmessage.png[Trace 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.

[source,java]
.Update the `GreetingProvider` class; 1) Add @Traced to the `GreetingProvider` class and 2) Remove @Traced from the `getMessage` method:
----
@Traced // <1>
@ApplicationScoped
public class GreetingProvider {
...

    String getMessage() { // <2>
        return message.get();
    }
----
<1> This will enable tracing for all class methods, except for the constructor and methods that are private.
<2> Remove @Traced for the `getMessage` method.

[source,bash]
.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"
[
...
  "io.helidon.examples.quickstart.mp.greetingprovider.getmessage", // <1>
...
]
----
<1> The service has the same set of span names as above, since `getmessage` was the only method called in this bean.

Next, invoke HTTP PUT to change the greeting, which will cause `setMessage` to be called.

[source,bash]
Invoke the endpoints and check the response:
----
curl -i -X PUT -H "Content-Type: application/json" -d '{"greeting": "Hi"}'  http://localhost:8080/greet/greeting // <1>
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", // <2>
  "put:io.helidon.examples.quickstart.mp.greetresource.updategreeting", // <3>
  "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.

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

NOTE: Methods invoked directly by your code are not enabled for tracing, even if you explicitly annotate them with @Traced.
Tracing only works for methods invoked on CDI beans. See the example below.

[source,java]
.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);
    }

    @Traced // <1>
    String getMessage() {
        return getMessage2();
    }

    @Traced  // <2>
    String getMessage2() {
        return message.get();
    }

    void setMessage(String message) {
        this.message.set(message);
    }
}
----
<1> The `getMessage` method will be traced since it is externally invoked by `GreetResource`.
<2> The `getMessage2` method will not be traced, even with the @Traced annotation, since it is called internally by `getMessage`.

[source,bash]
.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"
...
[
...
  "io.helidon.examples.quickstart.mp.greetingprovider.getmessage", // <1>
...
]
----
<1> The `getMessage` method is traced, but `getMessage2` is not.

=== Tracing across services

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

[source,bash,subs="attributes+"]
.Run the Maven archetype:
----
mvn archetype:generate -DinteractiveMode=false \
    -DarchetypeGroupId=io.helidon.archetypes \
    -DarchetypeArtifactId=helidon-quickstart-mp \
    -DarchetypeVersion={helidon-version} \
    -DgroupId=io.helidon.examples \
    -DartifactId=helidon-quickstart-mp-2 \
    -Dpackage=io.helidon.examples.quickstart.mp
----

[source,bash]
.The project will be built and run from the `helidon-quickstart-mp` directory:
----
cd helidon-quickstart-mp-2
----

[source,xml]
.Add the following dependency to `pom.xml`:
----
<dependency>
  <groupId>io.helidon.tracing</groupId>
  <artifactId>helidon-tracing-zipkin</artifactId>
</dependency>
----

[source,bash]
.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
----

[source,bash]
.Build the application, skipping unit tests, then run it:
----
mvn package -DskipTests=true
java -jar target/helidon-quickstart-mp-2.jar
----

[source,bash]
.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!"
}
----

==== 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.

[source,java]
.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; // <1>

  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") // <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();
  }
}
----
<1> This is the `WebTarget` needed to send a request to the second service at port `8081`.
<2> This is the new endpoint that will call the second service.


[source,bash]
.Build and run the application, then invoke the endpoint and check the response:
----
curl -i http://localhost:8080/greet/outbound // <1>
...
{
  "message": "Hello From MP-2 World!" // <2>
}
----
<1> The request went to the service on `8080`, which then invoked the service at `8081` to get the greeting.
<2> 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
image::guides/12_tracing_top_2_services.png[Traces]

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

.Tracing across multiple services detail view
image::guides/12_tracing_detail_2_services.png[Traces]

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 Zipkin from a Helidon application running in Kubernetes.

[source,bash]
.Add the following line to `META-INF/microprofile-config.properties`:
----
tracing.host=zipkin
----

[source,bash]
.Stop the application and build the docker image for your application:
----
docker build -t helidon-tracing-mp .
----

==== Deploy Zipkin into Kubernetes

[source,yaml]
.Create the Kubernetes YAML specification, named `zipkin.yaml`, with the following contents:
----
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
----

[source,bash]
.Create the Zipkin pod and ClusterIP service:
----
kubectl apply -f ./zipkin.yaml
----

[source,bash]
.Create a Zipkin external server and expose it on port 9142:
----
kubectl expose pod  zipkin --name=zipkin-external --port=9412 --target-port=9411 --type=LoadBalancer // <1>
----
<1> 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.


==== Deploy your Helidon application into Kubernetes

[source,yaml]
.Create the Kubernetes YAML specification, named `tracing.yaml`, with the following contents:
----
kind: Service
apiVersion: v1
metadata:
  name: helidon-tracing // <1>
  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 // <2>
  template:
    metadata:
      labels:
        app: helidon-tracing
        version: v1
    spec:
      containers:
        - name: helidon-tracing
          image: helidon-tracing-mp
          imagePullPolicy: IfNotPresent
          ports:
            - containerPort: 8080
----
<1> A service of type `NodePort` that serves the default routes on port `8080`.
<2> A deployment with one replica of a pod.

[source,bash]
.Create and deploy the application into Kubernetes:
----
kubectl apply -f ./tracing.yaml
----

==== Access your application and the Zipkin trace

[source,bash]
.Get the application service information:
----
kubectl get service/helidon-tracing
----

[source,bash]
----
NAME             TYPE       CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
helidon-tracing   NodePort   10.99.159.2   <none>        8080:31143/TCP   8s // <1>
----
<1> A service of type `NodePort` that serves the default routes on port `31143`.

[source,bash]
.Verify the tracing endpoint using port `31143`, your port will likely be different:
----
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.


==== Cleanup

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

[source,bash]
.Delete the Kubernetes resources:
----
kubectl delete -f ./zipkin.yaml
kubectl delete -f ./tracing.yaml
kubectl delete service zipkin-external
docker rm -f zipkin
----

== Summary

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

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


Refer to the following references for additional information:

- MicroProfile OpenTracing specification at https://github.com/eclipse/microprofile-opentracing/releases/tag/1.3
- MicroProfile OpenTracing Javadoc at https://javadoc.io/doc/org.eclipse.microprofile.opentracing/microprofile-opentracing-api/1.3
- Helidon Javadoc at https://helidon.io/docs/latest/apidocs/index.html?overview-summary.html




