Introduction

The code here tries to mimic a relatively likely production system. The mimiced system is supposed contain a plethora of bugs, anti-patterns, memory hogs, oddities, performance issues and in general be less than ideal. It serves as a sandbox, or playground to demonstrate how to troubleshoot various issues.

This project implements a fake business application, that gets request, and produces results.

sequenceDiagram
    actor User
    participant Computer
    participant WebAppServer
    participant BusinessApplication
    participant Backend
    User-->Computer: Action
    Computer->>WebAppServer: Do request
    note right of WebAppServer: JVM
    rect rgb(200,200,200,0.1)
      par Produces JFR event
        WebAppServer->>BusinessApplication: Invoke business logic
      and 
        opt Crashes
          BusinessApplication->>Backend: Do business
        end
        Backend->>BusinessApplication: Do other business
        BusinessApplication->>WebAppServer: Response
      end
      
    end
    WebAppServer->>Computer: Result

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❗ Disclaimer: This code contains both subtle and not so subtle bugs -- that is its purpose.

Motivations and objective

• produce JFR events, to learn JMC and try out stuff
• life-like env. to set JFR properties and arguments to get away from simple examples like: java -XX:StartFlightRecording Example.java
• reproducible executions; requests to the application are created from actual log files
• recreate bugs or weird behaviour
• has different web application servers (Micronaut, Jetty, will add WLS) in order to test where f.i. JFR VM properties are set

Possible scenarios

💣 crash "randomly" for learning purposes -- not just java Crash.java

⌚ find memory leaks, bottlenecks, etc

📊 create life-like JFR event examples, to not only create "TestEvent" and the likes

📈 using JConsole to remote JVM via ssh tunneling

📼 JFR remote recording stream to containerized servers

☕ create multi-JDK environments (JDK8 combined with JDK17)

Overview

flowchart TD
  nf([netflow_data logs]) --- Client
  WebClient --> appserver
  CliClient --> backend
  subgraph client [Client Components]
    Client --> WebClient
    Client --> CliClient
  end
  subgraph container [Server Components]
  subgraph appserver [Application Servers]
    JettyServer
    MicronautServer
  end
  appserver --> backend
  subgraph backend [Backend]
    BusinessLogic --- bd[(Backend)]
  end
  end
  style container fill:#c3a64724
  click Client "https://github.com/jaokim/inside-java-dumpster/tree/main/Client"
  click nf "https://github.com/jaokim/inside-java-dumpster/tree/main/Client"
  click WebClient "https://github.com/jaokim/inside-java-dumpster/tree/main/WebClient"
  click CliClient "https://github.com/jaokim/inside-java-dumpster/tree/main/CliClient"
  click BusinessLogic "https://github.com/jaokim/inside-java-dumpster/tree/main/BusinessLogic"
  click bd "https://github.com/jaokim/inside-java-dumpster/tree/main/Backend"
  click MicronautServer "https://github.com/jaokim/inside-java-dumpster/tree/main/MicronautServer"
  click JettyServer "https://github.com/jaokim/inside-java-dumpster/tree/main/JettyServer"

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The diagram above gives a context for most of the components involved. There is however also the OutsideDumpster which is included in each of the server components. This holds classes specific for the sandbox, and is used to aid in creating buggy behavior and disable/enable it in "production".

An example test-run

flowchart LR
  subgraph Client [Client terminal]
    WebClient["webclient http://jvm/business/"]
    jcmd["jcmd JFR.start"]
    JConsole
  end
  subgraph Server [Server terminal]
    subgraph JVM
      ApplicationServer
      JFR
    end
  end
  WebClient -->|request| ApplicationServer
  jcmd -->|record| JFR
  JConsole -->|control| JVM
  style JVM fill:#e0e0e9dd

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Preferable you'd want a remote machine to run the server JVM on, but it works with an all local setup.

• You need atleast JDK17.

Check out all the code and build using Maven (I might supply pre-built binairies at some point). Start two terminals (has been tested on cygwin).

In terminal 1, start the Micronaut Webserver

sh ./runmicronaut.sh

In terminal 2, start JConsole and connnect to the Micronaut JVM

jconsole &

Then, start the webclient script to create network requests.

sh runwebclient.sh

The runwebclient script first starts a delayed JFR recording for 60 seconds, and then produces network request for atleaset 60 seconds. When done, the webclient should stop, and you should have a JFR recording to analyze (or a crashlog!).

Excercise 1

Find out which service is the slowest, and why. When you've found the likely culprit, set it as non-buggy in JConsole, and do another test run.

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If you're looking for code for my old blog posts at inside.java, go look in the tag inside.java