Pods running Java consider entire node's memory for heap allocation with MicroOS

[knuurr]

We moved some of our workload from AWS EKS to Hetzner, courtesy of this Terraform module.

However our Java-based application experiences OOM conditions far more frequently than on AWS.

Heap is reported as MaxHeapSize = 92341796864 bytes. This is ~86 GB (92341796864 / 1024^3 ≈ 86 GB). So much of memory used by node itself (type is ccx53 in this case). This is not the case on EKS.

> java -XX:+PrintFlagsFinal -version | grep "MaxHeapSize"

Picked up JAVA_TOOL_OPTIONS: -Dsun.net.inetaddr.ttl=30 -Dsun.net.inetaddr.negative.ttl=0 -Dsun.net.inetaddr.cachePolicyProp=0 -XX:+UseContainerSupport -XX:InitialRAMPercentage=70 -XX:MaxRAMPercentage=70
   size_t MaxHeapSize                              = 92341796864                               {product} {ergonomic}
   size_t SoftMaxHeapSize                          = 92341796864                            {manageable} {ergonomic}
openjdk version "21.0.7" 2025-04-15 LTS
OpenJDK Runtime Environment Corretto-21.0.7.6.1 (build 21.0.7+6-LTS)
OpenJDK 64-Bit Server VM Corretto-21.0.7.6.1 (build 21.0.7+6-LTS, mixed mode, sharing)
bash-4.2# 

bash-4.2# cat /proc/meminfo | grep ^Mem
MemTotal:       128792068 kB
MemFree:        97818936 kB
MemAvailable:   114766140 kB

we of course have resources set for our deployment, which - according to my knowledge - should constrain accessible resources for Pods:

      resources:
        limits:
          cpu: '10'
          memory: 5Gi
        requests:
          cpu: '3'
          memory: 5Gi

I know this might not exactly be Hetzner issue, or module issue, but I would like to know if someone else encountered similar issue and how they dealt with it.

Here's OS:

node-xxxxxxxx:~ # cat /etc/*release
NAME="openSUSE MicroOS"
# VERSION="20241226"
ID="opensuse-microos"
ID_LIKE="suse opensuse opensuse-tumbleweed microos sl-micro"
VERSION_ID="20241226"
PRETTY_NAME="openSUSE MicroOS"
ANSI_COLOR="0;32"
CPE_NAME="cpe:/o:opensuse:microos:20241226"
BUG_REPORT_URL="https://bugzilla.opensuse.org"
SUPPORT_URL="https://bugs.opensuse.org"
HOME_URL="https://www.opensuse.org/"
DOCUMENTATION_URL="https://en.opensuse.org/Portal:MicroOS"
LOGO="distributor-logo-MicroOS"