If you are getting started with Spring Cloud Sleuth OTel or Spring in general, start by reading this section. It answers the basic “what?”, “how?” and “why?” questions. It includes an introduction to Spring Cloud Sleuth OTel, along with installation instructions. We then walk you through building your first Spring Cloud Sleuth OTel application, discussing some core principles as we go.
1. Introducing Spring Cloud Sleuth OTel
Spring Cloud Sleuth OTel provides integration with OpenTelemetry SDK.
2. Developing Your First Spring Cloud Sleuth OTel based Application
This section describes how to develop a small “Hello World!” web application that highlights some of Spring Cloud Sleuth’s key features. We use Maven to build this project, since most IDEs support it. As the tracer implementation we’ll use OpenTelemetry.
|
You can shortcut the steps below by going to start.spring.io and choosing the "Web" and "Spring Cloud Sleuth" starters from the dependencies searcher. Doing so generates a new project structure so that you can start coding right away. |
2.1. Creating the POM
We need to start by creating a Maven pom.xml file.
The pom.xml is the recipe that is used to build your project.
Open your favorite text editor and add the following:
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.example</groupId>
<artifactId>myproject</artifactId>
<version>0.0.1-SNAPSHOT</version>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<!-- Use the latest compatible Spring Boot version. You can check https://spring.io/projects/spring-cloud for more information -->
<version>$2.6.14</version>
</parent>
<!-- Spring Cloud Sleuth requires a Spring Cloud BOM -->
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<!-- Provide the latest stable Spring Cloud release train version (e.g. 2020.0.0) -->
<version>${release.train.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
<!-- Spring Cloud Sleuth OTel requires a Spring Cloud Sleuth OTel BOM -->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-sleuth-otel-dependencies</artifactId>
<!-- Provide the version of the Spring Cloud Sleuth OpenTelemetry project -->
<version>${spring-cloud-sleuth-otel.version}</version>
<scope>import</scope>
<type>pom</type>
</dependency>
</dependencies>
</dependencyManagement>
<!-- You 'll need those to add OTel support -->
<repositories>
<repository>
<id>spring-snapshots</id>
<url>https://repo.spring.io/snapshot</url>
<snapshots><enabled>true</enabled></snapshots>
</repository>
<repository>
<id>spring-milestones</id>
<url>https://repo.spring.io/milestone</url>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>spring-snapshots</id>
<url>https://repo.spring.io/snapshot</url>
</pluginRepository>
<pluginRepository>
<id>spring-milestones</id>
<url>https://repo.spring.io/milestone</url>
</pluginRepository>
</pluginRepositories>
</project>The preceding listing should give you a working build.
You can test it by running mvn package (for now, you can ignore the “jar will be empty - no content was marked for inclusion!” warning).
| At this point, you could import the project into an IDE (most modern Java IDEs include built-in support for Maven). For simplicity, we continue to use a plain text editor for this example. |
2.2. Adding Classpath Dependencies
To add the necessary dependencies, edit your pom.xml and add the spring-boot-starter-web dependency immediately below the parent section. To use Sleuth with OpenTelemetry do the following.
<dependencies>
<!-- Boot's Web support -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<!-- Sleuth with Brave tracer implementation -->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-sleuth</artifactId>
<exclusions>
<!-- Exclude Brave (the default) -->
<exclusion>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-sleuth-brave</artifactId>
</exclusion>
</exclusions>
</dependency>
<!-- Add OpenTelemetry tracer -->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-sleuth-otel-autoconfigure</artifactId>
</dependency>
</dependencies>2.3. Writing the Code
To finish our application, we need to create a single Java file.
By default, Maven compiles sources from src/main/java, so you need to create that directory structure and then add a file named src/main/java/Example.java to contain the following code:
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.*;
import org.springframework.boot.autoconfigure.*;
import org.springframework.web.bind.annotation.*;
@RestController
@EnableAutoConfiguration
public class Example {
private static final Logger log = LoggerFactory.getLogger(Backend.class);
@RequestMapping("/")
String home() {
log.info("Hello world!");
return "Hello World!";
}
public static void main(String[] args) {
SpringApplication.run(Example.class, args);
}
}Although there is not much code here, quite a lot is going on. We step through the important parts in the next few sections.
The @RestController and @RequestMapping Annotations
Spring Boot sets up the Rest Controller and makes our application bind to a Tomcat port. Spring Cloud Sleuth with OTel tracer will provide instrumentation of the incoming request.
2.4. Running the Example
At this point, your application should work.
Since you used the spring-boot-starter-parent POM, you have a useful run goal that you can use to start the application.
Type SPRING_APPLICATION_NAME=backend mvn spring-boot:run from the root project directory to start the application.
You should see output similar to the following:
$ mvn spring-boot:run . ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \ ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ ... ....... . . . ....... . . . (log output here) ....... . . . ........ Started Example in 2.222 seconds (JVM running for 6.514)
If you open a web browser to localhost:8080, you should see the following output:
Hello World!
If you check the logs you should see a similar output
2020-10-21 12:01:16.285 INFO [backend,0b6aaf642574edd3,0b6aaf642574edd3] 289589 --- [nio-9000-exec-1] Example : Hello world!
You can notice that the logging format has been updated with the following information [backend,0b6aaf642574edd3,0b6aaf642574edd3.
This entry corresponds to [application name,trace id, span id].
The application name got read from the SPRING_APPLICATION_NAME environment variable.
Instead of logging the request in the handler explicitly, you could set logging.level.org.springframework.web.servlet.DispatcherServlet=DEBUG.
|
To gracefully exit the application, press ctrl-c.
3. Next Steps
Hopefully, this section provided some of the Spring Cloud Sleuth OTel basics and got you on your way to writing your own applications. If you are a task-oriented type of developer, you might want to jump over to spring.io and check out some of the getting started guides that solve specific “How do I do that with Spring?” problems. We also have Spring Cloud Sleuth OTel-specific “how-to” reference documentation.
Otherwise, the next logical step is to read Using Spring Cloud Sleuth OTel. If you are really impatient, you could also jump ahead and read about Spring Cloud Sleuth OTel features.