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🛬 Java Flight Recorder

The Java flight recorder (JFR) is a great tool to gather extensive insights into a running Java JRE. It's free and is shipped along every recent JDK (11+). The observability process here has two steps

  1. Record a Java Flight Recording of an application for given timeframe (e.g. 60s)
  2. Analyze the recording using JDK Mission Control

alt

Prepare the Petclinic

Add the following volume mount to the Petclinic Docker Compose:

services:
  petclinic:
    volumes:
      - ./../java-flight-recorder:/tmp/jfr

Afterwards, restart your Petclinic:

cd ~/o11y-workshop/spring-petclinic
docker-compose restart petclinic

📼 Create a flight recording

Create an on-demand recording inside the running Docker container.

docker exec -it spring-petclinic-petclinic-1 bash
JAVA_TOOL_OPTIONS="" jcmd $(pgrep java) JFR.start name=profile duration=60s filename=/tmp/jfr/petclinic-$(date '+%Y-%m-%d_%H-%M-%S').jfr settings=profile
JAVA_TOOL_OPTIONS="" jcmd $(pgrep java) JFR.check

Due to the directory mount, your JFR will appear in this directory. You can download the file via VSCode (Right click -> Download).

✨ Analyze a flight recording

Install JDK Mission Control on your local laptop. Open the downloaded JFR recording with JDK Mission Control.

🛬 Configure the continuous flight recorder

Before stress testing the app, we want to configure the JVM to write a Flight Recorder dump before exit. You can do so by supplying the following options to the JVM.

services:
  petclinic:
    environment:
      - JAVA_TOOL_OPTIONS=-XX:StartFlightRecording=disk=true,maxsize=128M,dumponexit=true,name=continuous,settings=default,filename=/tmp/jfr/petclinic-onexit.jfr

Restart your Petclinic instance

cd ~/o11y-workshop/spring-petclinic
docker-compose restart petclinic

Verify that the JAVA_TOOL_OPTIONS have been picked up by the JVM and that the flight recorder is recording. It should look like this in the logs:

spring-petclinic-petclinic-1   | Picked up JAVA_TOOL_OPTIONS: -XX:StartFlightRecording=disk=true,maxsize=128M,dumponexit=true,name=continuous,settings=default,filename=/tmp/jfr/petclinic-onexit.jfr
spring-petclinic-petclinic-1   | [0.381s][info][jfr,startup] Started recording 1.
spring-petclinic-petclinic-1   | [0.381s][info][jfr,startup]
spring-petclinic-petclinic-1   | [0.381s][info][jfr,startup] Use jcmd 1 JFR.dump name=continuous to copy recording data to file.

😰 Stress testing

🤡 Yet again the fun part begins. Let's stress test our petclinic instrumented with the Java Flight Recorder and see the difference in observability!

hey -n 40000 -c 300 "https://petclinic.$(hostname).workshop.o11ystack.org/owners?lastName=$(hostname)"
  • How is the application/host/database behaving?
  • What is the first limit that the application is hitting? Can we somehow raise it?
  • After increasing a limit, repeat the stress test

Activate one (or more) bugs in the application and repeat the stress test. How is the application coping with the load then?

curl "https://petclinic.$(hostname).workshop.o11ystack.org/bugs/memory"
curl "https://petclinic.$(hostname).workshop.o11ystack.org/bugs/cpu"
curl "https://petclinic.$(hostname).workshop.o11ystack.org/bugs/locking"