jerboaa/jdk-17-container-detection

Deployment files for the JDK 17 cgroups v2 container detection minikube demo

OpenJDK 17 Container Detection Demo

This repository contains resource files used for the OpenJDK 17 container detection screencast illustrating cgroups v2 support on an Red Hat Enterprise Linux 9 system with Minikube installed.

Demo Application Deployment

In order to re-recreate the undertow deployment use:

$ git clone https://github.com/jerboaa/jdk-17-container-detection
$ cd jdk-17-container-detection
$ kubectl create -f fedora-undertow-jdk17.yaml && \
  kubectl expose deployment fedora-undertow-jdk17 --type=LoadBalancer --port=8080 && \
  kubectl get service fedora-undertow-jdk17

Access the endpoint via the external IP address (shown via the last kubectl get service command). For example:

$ curl -w '\n' http://10.109.124.25:8080
Hello World

Pod Name Helpers

In order to get the pod name of the deployed application, one can use this trick:

$ kubectl get pods -l app=fedora-undertow-jdk17 -o custom-columns=POD:.metadata.name
POD:
-------------------------------------
fedora-undertow-jdk17-c667567cf-5c6jk

Using this, we can define an alias to get the pod name of the current deployment regardless how often we redeploy:

$ alias fedora-undertow-jdk17-pod='kubectl get pod -l app=fedora-undertow-jdk17 -o custom-columns=POD:.metadata.name | tail -n1'
$ fedora-undertow-jdk17-pod
fedora-undertow-jdk17-c667567cf-5c6jk

Used JAVA_OPTS

The demo uses the following two options for a) container trace logging and b) gc info logging.

JVM Option	Description
-Xlog:os+container=trace	Turns on container trace level logging
-Xlog:gc=info	Turns on GC info level logging

Describe Kubernetes Deployment

In order to see resource quotas on the Kubernetes level, describing the deployment can be useful:

$ kubectl describe deployment fedora-undertow-jdk17

Inspecting Container Trace Logs

In order to see full logs of the deployed pod use (uses alias fedora-undertow-jdk17-pod defined above):

$ kubectl logs --tail=-1 $(fedora-undertow-jdk17-pod)
[0.026s][trace][os,container] OSContainer::init: Initializing Container Support
[0.028s][debug][os,container] Detected cgroups v2 unified hierarchy
[0.028s][trace][os,container] Path to /memory.max is /sys/fs/cgroup//memory.max
[0.028s][trace][os,container] Raw value for memory limit is: 2147483648
[0.028s][trace][os,container] Memory Limit is: 2147483648
[0.028s][info ][os,container] Memory Limit is: 2147483648
[0.028s][trace][os,container] Path to /cpu.max is /sys/fs/cgroup//cpu.max
[0.028s][trace][os,container] Raw value for CPU quota is: 300000
[0.028s][trace][os,container] CPU Quota is: 300000
[0.028s][trace][os,container] Path to /cpu.max is /sys/fs/cgroup//cpu.max
[0.029s][trace][os,container] CPU Period is: 100000
[0.029s][trace][os,container] Path to /cpu.weight is /sys/fs/cgroup//cpu.weight
[0.029s][trace][os,container] Raw value for CPU shares is: 39
[0.029s][trace][os,container] Scaled CPU shares value is: 1024
[0.029s][debug][os,container] CPU Shares is: 1024
[0.029s][trace][os,container] CPU Quota count based on quota/period: 3
[0.029s][trace][os,container] CPU Share count based on shares: 1
[0.029s][trace][os,container] OSContainer::active_processor_count: 3
[0.029s][trace][os,container] CgroupSubsystem::active_processor_count (cached): 3
[0.036s][trace][os,container] CgroupSubsystem::active_processor_count (cached): 3
[0.041s][info ][gc          ] Using G1

Restricting this to the first 10 lines of log output will show the relevant container trace output. Feel free to adjust the -nXX option to your needs:

$ kubectl logs --tail=-1 $(fedora-undertow-jdk17-pod) | head -n10
[0.020s][trace][os,container] OSContainer::init: Initializing Container Support
[0.021s][debug][os,container] Detected cgroups v2 unified hierarchy
[0.021s][trace][os,container] Path to /memory.max is /sys/fs/cgroup//memory.max
[0.021s][trace][os,container] Raw value for memory limit is: 2147483648
[0.021s][trace][os,container] Memory Limit is: 2147483648
[0.021s][info ][os,container] Memory Limit is: 2147483648
[0.021s][trace][os,container] Path to /cpu.max is /sys/fs/cgroup//cpu.max
[0.022s][trace][os,container] Raw value for CPU quota is: 300000
[0.022s][trace][os,container] CPU Quota is: 300000
[0.022s][trace][os,container] Path to /cpu.max is /sys/fs/cgroup//cpu.max

Inspecting GC Info Logs

In order to see the GC algorithm in use on the deployed pod (uses alias fedora-undertow-jdk17-pod defined above):

$ kubectl logs --tail=-1 $(fedora-undertow-jdk17-pod) | grep Using
[0.007s][info ][gc          ] Using G1

VM.info JCMD

A running JVM can be inspected for example via the VM.info JCMD. For example to see the full VM.info output use (note that the deployed application runs as PID 1):

$ kubectl exec $(fedora-undertow-jdk17-pod) -- jcmd 1 VM.info
1:
#
# JRE version: OpenJDK Runtime Environment 21.9 (17.0.2+8) (build 17.0.2+8)
# Java VM: OpenJDK 64-Bit Server VM 21.9 (17.0.2+8, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, g1 gc, linux-amd64)

---------------  S U M M A R Y ------------

Command Line: -Xlog:gc=info -Xlog:os+container=trace /deployments/undertow-servlet.jar

Host: QEMU Virtual CPU version 2.5+, 4 cores, 2G, Fedora release 35 (Thirty Five)
Time: Tue Feb 22 13:35:56 2022 UTC elapsed time: 64.876037 seconds (0d 0h 1m 4s)

---------------  P R O C E S S  ---------------

Heap address: 0x00000000e0000000, size: 512 MB, Compressed Oops mode: 32-bit

CDS archive(s) mapped at: [0x0000000800000000-0x0000000800be4000-0x0000000800be4000), size 12468224, SharedBaseAddress: 0x0000000800000000, ArchiveRelocationMode: 0.
Compressed class space mapped at: 0x0000000800c00000-0x0000000840c00000, reserved size: 1073741824
Narrow klass base: 0x0000000800000000, Narrow klass shift: 0, Narrow klass range: 0x100000000
[...]

In order to only see the cgroup information, use something like this:

$ kubectl exec $(fedora-undertow-jdk17-pod) -- jcmd 1 VM.info | grep -A13 '(cgroup)'
container (cgroup) information:
container_type: cgroupv2
cpu_cpuset_cpus: not supported
cpu_memory_nodes: not supported
active_processor_count: 3
cpu_quota: 300000
cpu_period: 100000
cpu_shares: 1024
memory_limit_in_bytes: 2147483648
memory_and_swap_limit_in_bytes: 2147483648
memory_soft_limit_in_bytes: unlimited
memory_usage_in_bytes: 181694464
memory_max_usage_in_bytes: not supported