138 lines
4.1 KiB
Markdown
138 lines
4.1 KiB
Markdown
## Datadog Java Tracer
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### Motivations
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The Datadog Java Tracer is an OpenTracing-compatible tracer. It provides all resources needed to instrument your code.
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Opentracing introduces the concept of the *span*. A span is *timed operation* representing an action in the code.
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The span can *be linked together*. And a trace is a list of spans, each related to the same top action/operation.
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Let's see an example. When a client does a request on a Http Endpoint, asking for some BD resources,
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Opentracing provides a way for measuring the time consumed for each operation:
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````
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TRACE:
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client ---> HTTP Endpoint ---> DB Query/Result ---> Custom processing ---> client
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SPAN 1 (Root Span) ................................................... (end) - 200ms
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|--------SPAN 2 (Child of 1).................................(end) - 100ms
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|-----------SPAN 3 (Child of 2).(end) - 50 ms
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|----------------------------------------SPAN 4 (Child of 2)..(end) - 50 ms
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````
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This shows a very simple example of how works [Opentracing](http://opentracing.io/).
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Here, the tracer produces a trace composed of 4 spans, each representing a specific action.
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### How to load the Datadog Tracer (DDTrace) in the project?
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The current implementation uses the trace-resolver feature provides by Opentracing.
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That means you can add and load the tracer using a Java Agent directly with the JVM.
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And then, the DDTrace can be configured using a YAML file: `dd-trace.yaml`.
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By default, the DDTrace tries to reach a local Datadog Agent, but it can change by settings a different
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location in the config file. Please, refer to the latest configuration template: [dd-trace.yaml](src/main/resources/dd-trace.yaml)
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### How to use the Datadog Tracer (DDTrace) to instrument the code?
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Once, the DDTrace is loaded, you can start to instrument your code using:
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* The `@Trace` annotation,
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* Or the Opentracing SDK.
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This agent is build on the top of the [Open-Tracing contributions](https://github.com/opentracing-contrib/) and the [Datadog
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tracer](https://github.com/DataDog/dd-trace-java).
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At the moment, the Datadog Java Agent supports the following framework and librairies:
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* Databases
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* JDBC connections
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* Mongo
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* Elasticsearch
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* Web servers and clients
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* Spring Boot
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* Jetty Server
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* Tomcat Servlet
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* Apache HTTP Client
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* OkHttp
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* Queueing
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* JMS
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* Third-party
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* AMS SDK Client
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#### Instrument your code
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Here are the instructions.
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Before start, make sure you have a running Datadog Agent with the [APM feature enabled](http://docs.datadoghq.com/tracing/).
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1. Download the latest Datadog Java Agent version: https://mvnrepository.com/artifact/com.datadoghq/dd-java-agent.
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```pom.xml
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<dependency>
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<groupId>com.datadoghq</groupId>
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<artifactId>dd-java-agent</artifactId>
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<version>${dd-trace.version}</version>
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</dependency>
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```
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2. Add to the JVM the agent. This can be done by editing the command line or via the pom file.
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```pom.xml
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-surefire-plugin</artifactId>
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<version>2.20</version>
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<configuration>
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<includes>
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<include>*Test.java</include>
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</includes>
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<excludes>
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<exclude>ElasticSearchInstrumentationTest.java</exclude>
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</excludes>
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<forkCount>3</forkCount>
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<reuseForks>false</reuseForks>
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<argLine>-javaagent:${M2_REPO}/com/datadoghq/dd-java-agent/${dd-trace.version}/dd-java-agent-${dd-trace.version}.jar</argLine>
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<workingDirectory>target/FORK_DIRECTORY_${surefire.forkNumber}</workingDirectory>
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</configuration>
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</plugin>
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```
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### How it's work
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### Dig deeper
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Du coup le Readme.md de `java-trace` il faut un truc plutot simple qui expliqe que c la
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librarie opentracing compliant de Datadog. Il faut expliquer aussi le resolver et son fichier `.yaml`
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[10:41]
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Prend peut etre exemple aussi sur une autre lib opentracing compliant
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[10:41]
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Peut etre expliquer ce que c’est un tracer, un span et un ou deux exemple d’instrumentation a la mano¡¡ |