README.md

Drill agent component

This module contains the native agent used to profile a java application and report the results to Drill4J admin services.

Modules

• bootstrap: See description below
• java-agent: Java-agent itself
• pt-runner: Module with scripts to run demo application

Classes structure

• commonMain: consist of empty expected classes (transformers, plugin related and request-processing related classes) and few utility classes (serialization functions and ClassSource models)
• jvmMain: classes for initial class scanning and transformation
  • com.epam.drill.agent.classloading: initial class scanning without transformation
  • com.epam.drill.agent.instrument: java-classes instrumentation for http-headers processing
    • com.epam.drill.agent.instrument.Transformer: ServletContextListeneer instrumentation for web-app classes initial scanning
  • com.epam.drill.request: http-request headers processing (mainly related with drill-session-id)
• nativeMain:
  • com.epam.drill.agent: agent configuration and state classes
  • com.epam.drill.agent.classloading: stubs to call jvm-part of the same package (using KNI)
  • com.epam.drill.agent.instrument: stubs to call jvm-part of the same package (using KNI)
  • com.epam.drill.core:
    • Starter.kt: JVMTI entrypoint, call agent configuration classes and registers hooks on JVM initialization and class-loading
    • CallbackRegister.kt: Internal callback initialization
    • SymbolsRegister.kt: Native functions to call from plugins using com.epam.drill.plugin.api.Native class
  • com.epam.drill.core.callbacks.vminit: Agent initialization callbacks (connects to admin, reads package settings)
  • com.epam.drill.core.callbacks.classloading: Classloading callback (applies default transformers from agent-jvm-part and transformers from loaded plugins)
  • com.epam.drill.core.plugin.loader: Plugin load and initialization related classes

Run demo

To run the demo application (Petclinic) with a built agent following command may be used:

./gradlew :pt-runner:run 

The Petclinic application will be started on port 8080, and agent will be configured to connect to the admin back-end on port 8090.

Module bootstrap

Problems before:

• Need to update version agent, but restart of app with agent takes a lot of time, and it breaks CI/CD process. We can find the moment when app will be restarted, but it is not convenient.
• On Windows, we can't remove files(agent) while process is running

Bootstrap solve these problems, now we can change dirs to java agent. After restart app we will use new java agent.