There are a few factors that could explain why the MaxHeapSize for your Java application is less than the expected 80% of your container's memory request in Kubernetes. Here's a detailed breakdown of possible causes:

1. Container Memory Limit vs. Memory Request In Kubernetes, memory requests and limits are two separate concepts. Your memory request (62000Mi) only guarantees that amount of memory to your container if sufficient resources are available. However, the JVM uses the memory limit (if set) to calculate the MaxRAMPercentage and InitialRAMPercentage values.

If the memory limit is not explicitly set, Kubernetes defaults to the node's capacity or allocatable memory. On a 64GB node, the allocatable memory is typically less than 64GB due to system and Kubernetes overhead.

To fix this, ensure you have set an explicit memory limit in your pod spec, like so:

yaml Copy code resources: requests: memory: "62000Mi" limits: memory: "62000Mi" 2. Overhead of the Kubernetes Environment Kubernetes reserves some memory for itself (kubelet, kube-proxy, etc.), which reduces the memory available to containers.

Additionally, your container may be limited by the CGroup configuration on the worker node. You can verify the memory available to your container by checking the following file inside the container:

bash Copy code cat /sys/fs/cgroup/memory/memory.limit_in_bytes If this value is less than 62000Mi, the JVM will use this lower value to calculate heap size.

3. Other JVM Memory Regions The JVM uses memory not just for the heap but also for other regions like Metaspace, Thread Stacks, Code Cache, and Direct Buffers. These regions typically consume a significant portion of memory, leaving less available for the heap. On Java 11, common overhead includes: Metaspace: Can grow dynamically but often starts at around 100-300 MB. Thread Stack: Depends on the number of threads and the stack size (default: 1MB per thread). Code Cache: Usually a few hundred MB. For better control, you can explicitly set memory for these regions using JVM options like -XX:MaxMetaspaceSize and -Xss.
4. VMWare Dynamic Memory Allocation If your Kubernetes nodes are running on VMWare with dynamic memory allocation, the underlying memory reported to the JVM might be less than expected due to hypervisor-level adjustments. This dynamic behavior can cause the JVM to miscalculate the heap size because it bases its calculations on available memory reported by the OS.
5. JVM Implementation and Defaults The behavior of -XX:MaxRAMPercentage and -XX:InitialRAMPercentage can vary slightly depending on the exact JVM implementation. Ensure you're using a supported and consistent distribution (e.g., OpenJDK 11). The default container detection logic in Java 11 should respect the limits set by Kubernetes, but issues can arise in specific environments or older patch versions of Java 11.