83 lines
2.9 KiB
Markdown
83 lines
2.9 KiB
Markdown
## Dropwizard-mongo-client example
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### Purpose
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This project aims at demonstrating how to instrument legacy code based on:
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* the Dropwizard framework
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* a Mongo database.
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We also demonstrate user cross-process tracing through the `TracedClient` example.
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### Run the demo
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#### Prerequisites
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1. Make sure that you have a local mongo database running (hostname: `localhost`, port: `27017`).
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2. No process holding the 8080 and the 8081 port, they are used by the Dropwizard server.
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If you're using Docker, you can run a mongo instance as follow:
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```bash
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docker run -it --rm -p 27017:27017 --name mongo -d mongo
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```
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#### Run the application
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If you want to enable tracing you have to launch the application with the Datadog java agent.
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First, get the latest version of the dd-java-agent:
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*NOTE:* While in beta, the latest version is best found on the [Snapshot Repo](https://oss.jfrog.org/artifactory/oss-snapshot-local/com/datadoghq/).
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```
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# download the latest published version:
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wget -O dd-java-agent.jar 'https://search.maven.org/remote_content?g=com.datadoghq&a=dd-java-agent&v=LATEST'
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```
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Then, build the app add the agent to the JVM. That can be done as follow:
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```
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cd path/to/dd-trace-examples/dropwizard-mongo-client
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./gradlew clean shadowJar
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java -javaagent:/path/to/dd-java-agent.jar -jar build/libs/dropwizard-mongo-client-demo-all.jar server
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```
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### Generate traces
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#### With your web browser
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Once the application runs. Go to the following url:
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* [http://localhost:8080/demo/add?title=some-book-title&isbn=1234&page=42]()
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* [http://localhost:8080/demo/]()
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Then get back to Datadog and wait a bit to see a trace coming.
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#### Cross process tracing: with the provided `TracedClient` class
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Runs the `TracedClient` class with the java agent as explained above.
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In that case, we instrument the `OkHttpClient` and you then observe a similar trace as the example just above but with the client as the originating root span.
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Cross process tracing is working thanks to headers injected on the client side that are extracted on the server. If you want to understand more you can refer to the [opentracing documentation](http://opentracing.io/documentation/pages/api/cross-process-tracing.html).
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*A trace example*
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To run the distributed example, first start the dropwizard app, the mongo db and finally run the `main` from `com.example.helloworld.client.TracedClient`
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### How did we instrument this project?
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#### Auto-instrumentation with the `dd-trace-agent`
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The instrumentation is entirely done by the datadog agent which embed a set of rules that automatically recognizes & instruments:
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- The Java servlet filters
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- The Mongo client
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- The OkHTTP client
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- The `@Trace` annotation
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The Datadog agent embeds the [open tracing java agent](https://github.com/opentracing-contrib/java-agent).
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We strongly recommend you to refer to the [Datadog Agent documentation](../../dd-java-agent) if you want to dig deeper.
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