From 7881d7dd4213837ea547489f0d8fa472d680f49e Mon Sep 17 00:00:00 2001
From: Guillaume Polaert <gpolaert@gmail.com>
Date: Wed, 24 May 2017 12:00:46 +0200
Subject: [PATCH] First version

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