I Code Java 2022 Demo

This project is used to illustrate resilience problems that can occur in java applications and show how you can troubleshoot them.

• Memory Leaks
• Thread contention
• High CPU usage

Build

You can build the project using maven mvn clean verify or the maven wrapper included in this repo mvnw clean verify

Run the service

Run the jar using java: java -Xmx256M -XX:+HeapDumpOnOutOfMemoryError -XX:+FlightRecorder -XX:StartFlightRecording=filename=flight.jfr -jar target/icj-demo-0.0.1-SNAPSHOT.jar

Load Tests

To run the load tests against a local instance, open the jmx file with jmeter and enable the appropriate thread group

Replicating the Problems

Memory Leak

• Start up the java app. Make sure -XX:+HeapDumpOnOutOfMemoryError is enabled
• Enable the "Memory Leak" group in the load test
• Run the load test until the jvm runs out of memory
• (Optional) Take a manual heap dump using jmap -dump:live,file=<file>.hprof <pid> or jcmd <pid> GC.heap_dump <file>.hprof
• Inspect the heap dumps with Eclipse Memory Analyzer

Thread Contention

• Start up the java app.
• Enable the "Slow" group in the load test
• Run the load test for a few minutes. You should see response times in the jmeter summary view dropping.
• Take a manual thread dump using kill -3 <pid> or jstack <pid> > threads.tdump
• Stop the load test after taking the thread dump
• Analyze the thread dump using your IDE or an online tool like fastthread.io
• (Optional) You can lso analyze the impact of the slow endpoint using java flight recorder

High CPU usage

• Start up the java app. Make sure -XX:+FlightRecorder -XX:StartFlightRecording=filename=flight.jfr is enabled.
• Enable the "Busy" group in the load test
• Run the load test for a few minutes.
• (Optional) Start another flight recording using jcmd jcmd <pid> JFR.start filename=<file>.jfr. Stop it using jcmd <pid> JFR.stop
• Stop the java process (This ensures the flight recording started using jvm arguments is fully written to the output file)
• Inspect the Java Flight Recorder (jfr) file using your IDE or Java Mission Control