Is -XX:MaxRAMFraction=1 safe for production in a containered environment?

Question

Java 8/9 brought support for -XX:+UseCGroupMemoryLimitForHeap (with -XX:+UnlockExperimentalVMOptions). This sets -XX:MaxRAM to the cgr

Answer 1

We did some simple testing which showed that setting -XX:MaxRAM=$QUOTA and -XX:MaxRAMFraction=1 results in killed containers under load. The JVM allocates more than 900M heap, which is way too much. -XX:MaxRAMFraction=2 seems safe(ish).

Keep in mind that you may want to leave headroom for other processes like getting a debug shell (docker exec) or diagnostics in the container.

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Edit: we've written up what we've learned in detail in an article. Money quotes:

TL'DR: Java memory management and configuration is still complex. Although the JVM can read cgroup memory limits and adapt memory usage accordingly since Java 9/8u131, it’s not a golden bullet. You need to know what -XX:+UseCGroupMemoryLimitForHeap does and you need to fine tune some parameters for every deployment. Otherwise you risk wasting resources and money or getting your containers killed at the worst time possible. -XX:MaxRAMFraction=1 is especially dangerous. Java 10+ brings a lot of improvements but still needs manual configuration. To be safe, load test your stuff.

and

The most elegant solution is to upgrade to Java 10+. Java 10 deprecates -XX:+UseCGroupMemoryLimitForHeap (11) and introduces -XX:+UseContainerSupport (12), which supersedes it. It also introduces -XX:MaxRAMPercentage (13) which takes a value between 0 and 100. This allows fine grained control of the amount of RAM the JVM is allowed to allocate. Since +UseContainerSupport is enabled by default, everything should work out of the box.

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Edit #2: we've written a little bit more about -XX:+UseContainerSupport

Java 10 introduced +UseContainerSupport (enabled by default) which makes the JVM use sane defaults in a container environment. This feature is backported to Java 8 since 8u191, potentially allowing a huge percentage of Java deployments in the wild to properly configure their memory.