JEP [DRAFT]: Container aware Java

David Holmes david.holmes at
Fri Feb 16 02:33:03 UTC 2018

On 16/02/2018 4:30 AM, kedar mhaswade wrote:
> This appears useful.
> Will Runtime.getRuntime().availableProcessors() return the processors
> available to the container after this integration, or will a new API be
> provided? I have seen thread pools being misconfigured (e.g. it returns the
> number of processors available on the host which is far more than that of
> processors allotted by cgroups to the container) because of the confusion
> (or because of just using the non-container-aware code).

Depending on what you mean by "allotted" the VM has reported the actual 
set of CPU's available to the VM process (as can be configured by 
cpu_sets) since JDK 9. In JDK 10 quotas/shares are also used to 
approximate a notion of "available processors".


> Regards,
> Kedar
> On Thu, Feb 15, 2018 at 10:04 AM, Bob Vandette <bob.vandette at>
> wrote:
>>> On Feb 15, 2018, at 12:52 PM, Volker Simonis <volker.simonis at>
>> wrote:
>>> Sounds cool!
>>> Is this JEP only about providing the corresponding API or also about
>>> using it internally (within HotSpot and class library) to better adopt
>>> to environment the JVM is running in?
>> Thanks Volker.
>> I integrated JDK-8146115 into JDK 10 which allows Hotspot to adapt to the
>> container it’s running in.  The configuration that is examined includes
>> memory limits,
>> cpu count including cpu shares and quotas.
>> This JEP’s main focus is to provide an internal API that can be used by
>> JDK tools
>> such as JFR and JMX to export container statistics and configuration
>> data.  This JEP
>> does not include the JFR and JMX implementations.  They will hopefully
>> follow shortly after.
>> Bob.
>>> Either way, looking forward to see (and test) the first implementation
>> bits!
>>> Regards,
>>> Volker
>>> On Thu, Feb 15, 2018 at 6:07 PM, Bob Vandette <bob.vandette at>
>> wrote:
>>>> I’d like to re-propose the following JEP that will enhance the Java
>> runtime to be more container aware.
>>>> This will add an Internal Java API that will provide container specific
>> statistics.  Some of the initial goals
>>>> of the previous JEP proposal has been integrated into JDK 10 under an
>> RFE (JDK-8146115).
>>>> This JEP is now focused on providing a Java API that exports Container
>> runtime configuration and metrics.
>>>> Since the scope of this JEP have changed, I’m re-submitting it for
>> comment and endorsement.
>>>> JEP Issue:
>>>> Here’s a Text dump of the JEP contents for your convenience:
>>>> Summary
>>>> -------
>>>> Container aware Java runtime
>>>> Goals
>>>> -----
>>>> Provide an internal API that can be used to extract container specific
>> configuration and runtime statistics.  This JEP will only support Docker on
>> Linux-x64 although the design should be flexible enough to allow support
>> for other platforms and container technologies.  The initial focus will be
>> on Linux cgroups technology so that we will be able to easily support other
>> container technologies running on Linux in addition to Docker.
>>>> Non-Goals
>>>> ---------
>>>> It is not a goal of this JEP to support any platform other than Docker
>> container technology running on Linux x64.
>>>> Success Metrics
>>>> ---------------
>>>> Success will be measured by the improvement in information that will be
>> available to tools which visualize resource usage of containers that are
>> running Java processes.
>>>> Motivation
>>>> ----------
>>>> Container technology is becoming more and more prevalent in Cloud based
>> applications.  The Cloud Serverless application programming model motivates
>> developers to split large monolithic applications into 100s of smaller
>> pieces each running in thier own container.  This move increases the
>> importance of the observability of each running container process.  Adding
>> the proposed set of APIs will allow more details related to each container
>> process to be made available to external tools thereby improving the
>> observability.
>>>> Description
>>>> -----------
>>>> This enhancement will be made up of the following work items:
>>>> A. Detecting if Java is running in a container.
>>>> The Java runtime, as well as any tests that we might write for this
>> feature, will need to be able to detect that the current Java process is
>> running in a container.  A new API will be made available for this purpose.
>>>> B. Exposing container resource limits, configuration and runtime
>> statistics.
>>>> There are several configuration options and limits that can be imposed
>> upon a running container.  Not all of these
>>>> are important to a running Java process.  We clearly want to be able to
>> detect how many CPUs have been allocated to our process along with the
>> maximum amount of memory that the process has been allocated but there are
>> other options that we might want to base runtime decisions on.
>>>> In addition, since Container typically impose limits on system
>> resources, they also provide the ability to easily access the amount of
>> consumption of these resources.  The goal is to provide this information in
>> addition to the configuration data.
>>>> I propose adding a new jdk.internal.Platform class that will allow
>> access to this information.
>>>> Here are some of the types of configuration and consumption statistics
>> that would be made available:
>>>>     isContainerized
>>>>     Memory Limit
>>>>     Total Memory Limit
>>>>     Soft Memory Limit
>>>>     Max Memory Usage
>>>>     Current Memory Usage
>>>>     Maximum Kernel Memory
>>>>     CPU Shares
>>>>     CPU Period
>>>>     CPU Quota
>>>>     Number of CPUs
>>>>     CPU Sets
>>>>     CPU Set Memory Nodes
>>>>     CPU Usage
>>>>     CPU Usage Per CPU
>>>>     Block I/O Weight
>>>>     Block I/O Device Weight
>>>>     Device I/O Read Rate
>>>>     Device I/O Write Rate
>>>>     OOM Kill Enabled
>>>>     OOM Score Adjustment
>>>>     Memory Swappiness
>>>>     Shared Memory Size
>>>> Alternatives
>>>> ------------
>>>> There are a few existing tools available to extract some of the same
>> container statistics.  These tools could be used instead.  The benefit of
>> providing a core Java internal API is that this information can be expose
>> by current Java serviceability tools such as JMX and JFR along side other
>> JVM specific information.
>>>> Testing
>>>> -------
>>>> Docker/container specific tests should be added in order to validate
>> the functionality being provided with this JEP.
>>>> Risks and Assumptions
>>>> ---------------------
>>>> Docker is currently based on cgroups v1. Cgroups v2 is also available
>> but is incomplete and not yet supported by Docker. It's possible that v2
>> could replace v1 in an incompatible way rendering this work unusable until
>> it is upgraded.
>>>> Other alternative container technologies based on hypervisors are being
>> developed that could replace the use of cgroups for container isloation.
>>>> Dependencies
>>>> -----------
>>>> None at this time.

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