Demo 01 — Container-Aware Heap Sizing

Without UseContainerSupport, the JVM reads host RAM from /proc/meminfo and claims 25% of the node’s full memory — inside a container with a 512MB limit. Kubernetes OOMKills the pod within seconds.

What you’ll see

1. JVM without UseContainerSupport → reads host RAM → OOMKill simulation
2. UseContainerSupport + MaxRAMPercentage=75.0 → JVM respects the container limit
3. Live jcmd output comparing configured heap sizes

The fix

# ❌ Hardcoded — breaks when VPA or cluster admin resizes
-Xms512m -Xmx2048m

# ✅ Container-aware — scales automatically with the limit
-XX:+UseContainerSupport
-XX:MaxRAMPercentage=75.0
-XX:InitialRAMPercentage=50.0

Why 75%?

MaxRAMPercentage=75 leaves 25% for five other JVM memory regions that most teams forget:

Verify at runtime

jcmd <pid> VM.flags | grep -E "MaxHeap|RAMPercentage"

Reference

• Demo source
• Quarkus Configuration Reference