Agent inclusion in docker via Gradle/Jib... idea for doc

[alexvanboxel]

We are including the java agent now in our docker containers, it was a challenge wiring this in our Gradle builds. I'll include the useful snippets here, but this could be useful to include these snippets somewhere in some documentation. If someone tells me where it could live, I'll make a PR. Here are the snippets:

Add a dependency configuration in gradle:

configurations {
    agent
}

Add the dependency to the agent

dependencies {
    agent "io.opentelemetry.javaagent:opentelemetry-javaagent:0.13.0:all"
}

Jib automatically includes everything in src\main\jib. The container has the env variable OTEL_JAVAAGENT_ENABLED set to false by default.

jib {
    from {
        image = 'redacted/zulu-openjdk-alpine-with-fonts:1.0.8'
    }
    to {
        image = 'redacted/prod/dgc-core:' + project.version
    }
    container {
        appRoot = '/app'
        entrypoint = ['java', '-cp', '/app', '-XX:MaxMetaspaceSize=512m',
                      '-Djava.security.egd=file:/dev/./urandom',
                      '-javaagent:/app/WEB-INF/agent/otel-javaagent.jar',
                      '-Dotel.instrumentation.jdbc-datasource.enabled=false',
                      '-Dotel.instrumentation.servlet-filter.enabled=true',
                      '-Dotel.instrumentation.servlet-service.enabled=true',
                      'org.springframework.boot.loader.WarLauncher'
        ]
        environment = [
                'OTEL_JAVAAGENT_ENABLED':'false'
        ]
    }
}

Some tasks need to be included to hook into the lifecycle. We also reference that agent artifact in a run configuration (IntelliJ)

// Copy the OpenTelemetry agent to the Jib folder so it will be included in the
// docker image. It should also be available for local development (referenced
// from a run configuration).
task copyAgentJar(type: Copy) {
    from configurations.agent
    into "src/main/jib/app/WEB-INF/agent"
    rename { fileName -> "otel-javaagent.jar" }
}
compileJava.dependsOn copyAgentJar
clean.doFirst {
    delete "src/main/jib/app/WEB-INF/agent"
}

[trask]

hi @alexvanboxel! I think this would make a great example under https://github.com/open-telemetry/opentelemetry-java-instrumentation/tree/master/examples