Summary

In Java, the reported number of CPUs may be lower than the allocated number when running in containerized environments like Amazon ECS, Docker, or Kubernetes. This discrepancy can impact JVM processes, such as garbage collection, and the application's internal workings, as thread pools are often sized based on concurrency scaling factors like CPU core count. Consequently, underreporting the available CPU count can lead to performance issues.

In Bamboo, the JVM-reported CPU cores determine the number of concurrent threads launched. As a result, critical threads such as the PlanExec thread and other essential application components may experience low performance due to the presentation of a single CPU core.

Environment

• Bamboo Server hosted on Amazon ECS or other containerized environments/services like those backed by Docker & Kubernetes.
• Java

Diagnosis

The CPU core count can be checked at:

• Bamboo Administration >> Overview >> System Information >> (System Properties) Available processors

Alternatively, when generating a Support Zip, the application-properties/application.xml also contains the available processors:

    <available-processors>1</available-processors>

You can create the following Java showProc.java program inside your Bamboo container, compile it, and run it to output the number of processors seen by Java:

docker exec -i bamboo_container /bin/bash -c 'cd /tmp; cat > showProc.java; javac showProc.java; java showProc; rm showProc.java showProc.class' <<EOF
public class showProc {
   public static void main(String[] args) {
      System.out.print("Number of available processors: ");
      System.out.println( Runtime.getRuntime().availableProcessors());
   }
}
EOF

Number of available processors: 1

Cause

Amazon ECS:

The ECS agent forces the Docker's CpuShares setting always to be set for every container it runs, even if it's empty on the task definition. This negatively affects the performance of containers that use this information to configure their threading.

This can also be caused by leaving the cpu / CpuShares unset on the Task Definition.

More information: 

• CpuShares is always enforced to a minimum of 2 #1735
• Using Corretto in Amazon ECS with 1024 CPU units #191

Solution

Amazon ECS:

Set cpu / CpuShares on the Task Definition rather than leaving the default:

• Amazon ECS - Task Definition Parameters

That is also fixed on a recent release of AWS CDK.

Workaround

Add specific properties to Java

If the actual processor count is known, you can override the active processor count by adding JVM arguments. The following would set the processor count to 10.

Java 8:

-XX:+UnlockExperimentalVMOptions -XX:ActiveProcessorCount=10

Java 11 and later:

-XX:ActiveProcessorCount=10

See the below documentation on how to configure these depending on your Bamboo installation environment:

• Bamboo: Configuring your System Properties