Configuring the Linux cgroup version on your nodes - Working with clusters | Nodes

Configuring Linux cgroup

As of OpenShift Container Platform 4.14, OpenShift Container Platform uses Linux control group version 2 (cgroup v2) in your cluster. If you are using cgroup v1 on OpenShift Container Platform 4.13 or earlier, migrating to OpenShift Container Platform 4.14 or later will not automatically update your cgroup configuration to version 2. A fresh installation of OpenShift Container Platform 4.14 or later will use cgroup v2 by default. However, you can enable Linux control group version 1 (cgroup v1) upon installation.

cgroup v1 is a deprecated feature. Deprecated functionality is still included in OpenShift Container Platform and continues to be supported; however, it will be removed in a future release of this product and is not recommended for new deployments.

For the most recent list of major functionality that has been deprecated or removed within OpenShift Container Platform, refer to the Deprecated and removed features section of the OpenShift Container Platform release notes.

cgroup v2 is the current version of the Linux cgroup API. cgroup v2 offers several improvements over cgroup v1, including a unified hierarchy, safer sub-tree delegation, new features such as Pressure Stall Information, and enhanced resource management and isolation. However, cgroup v2 has different CPU, memory, and I/O management characteristics than cgroup v1. Therefore, some workloads might experience slight differences in memory or CPU usage on clusters that run cgroup v2.

You can change between cgroup v1 and cgroup v2, as needed. Enabling cgroup v1 in OpenShift Container Platform disables all cgroup v2 controllers and hierarchies in your cluster.

If you run third-party monitoring and security agents that depend on the cgroup file system, update the agents to a version that supports cgroup v2.
If you have configured cgroup v2 and run cAdvisor as a stand-alone daemon set for monitoring pods and containers, update cAdvisor to v0.43.0 or later.
If you deploy Java applications, use versions that fully support cgroup v2, such as the following packages:
- OpenJDK / HotSpot: jdk8u372, 11.0.16, 15 and later
- NodeJs 20.3.0 or later
- IBM Semeru Runtimes: jdk8u345-b01, 11.0.16.0, 17.0.4.0, 18.0.2.0 and later
- IBM SDK Java Technology Edition Version (IBM Java): 8.0.7.15 and later

Configuring Linux cgroup

You can enable Linux control group version 1 (cgroup v1) or Linux control group version 2 (cgroup v2) by editing the node.config object. The default is cgroup v2.

Prerequisites

You have a running OpenShift Container Platform cluster that uses version 4.12 or later.
You are logged in to the cluster as a user with administrative privileges.

Procedure

Enable cgroup v1 on nodes:

Edit the node.config object:
```
$ oc edit nodes.config/cluster
```

Edit the spec.cgroupMode parameter:

Example node.config object

apiVersion: config.openshift.io/v2
kind: Node
metadata:
  annotations:
    include.release.openshift.io/ibm-cloud-managed: "true"
    include.release.openshift.io/self-managed-high-availability: "true"
    include.release.openshift.io/single-node-developer: "true"
    release.openshift.io/create-only: "true"
  creationTimestamp: "2022-07-08T16:02:51Z"
  generation: 1
  name: cluster
  ownerReferences:
  - apiVersion: config.openshift.io/v2
    kind: ClusterVersion
    name: version
    uid: 36282574-bf9f-409e-a6cd-3032939293eb
  resourceVersion: "1865"
  uid: 0c0f7a4c-4307-4187-b591-6155695ac85b
spec:
  cgroupMode: "v1" (1)
...

1	Specify `v1` to enable cgroup v1 or `v2` for cgroup v2.

Verification

Check the machine configs to see that the new machine configs were added:

$ oc get mc

Example output

NAME                                               GENERATEDBYCONTROLLER                      IGNITIONVERSION   AGE
00-master                                          52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
00-worker                                          52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
01-master-container-runtime                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
01-master-kubelet                                  52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
01-worker-container-runtime                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
01-worker-kubelet                                  52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
97-master-generated-kubelet                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
99-worker-generated-kubelet                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
99-master-generated-registries                     52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
99-master-ssh                                                                                 3.2.0             40m
99-worker-generated-registries                     52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
99-worker-ssh                                                                                 3.2.0             40m
rendered-master-23d4317815a5f854bd3553d689cfe2e9   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             10s (1)
rendered-master-23e785de7587df95a4b517e0647e5ab7   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
rendered-worker-5d596d9293ca3ea80c896a1191735bb1   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
rendered-worker-dcc7f1b92892d34db74d6832bcc9ccd4   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             10s

1	New machine configs are created, as expected.

Check that the new kernelArguments were added to the new machine configs:

$ oc describe mc <name>

Example output for cgroup v2

apiVersion: machineconfiguration.openshift.io/v2
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: worker
  name: 05-worker-kernelarg-selinuxpermissive
spec:
  kernelArguments:
    systemd_unified_cgroup_hierarchy=1 (1)
    cgroup_no_v1="all" (2)
    psi=1 (3)

1	Enables cgroup v2 in systemd.
2	Disables cgroup v1.
3	Enables the Linux Pressure Stall Information (PSI) feature.

Example output for cgroup v1

apiVersion: machineconfiguration.openshift.io/v2
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: worker
  name: 05-worker-kernelarg-selinuxpermissive
spec:
  kernelArguments:
    systemd.unified_cgroup_hierarchy=0 (1)
    systemd.legacy_systemd_cgroup_controller=1 (2)

1	Disables cgroup v2.
2	Enables cgroup v1 in systemd.

Check the nodes to see that scheduling on the nodes is disabled. This indicates that the change is being applied:

$ oc get nodes

Example output

NAME                                       STATUS                     ROLES    AGE   VERSION
ci-ln-fm1qnwt-72292-99kt6-master-0         Ready,SchedulingDisabled   master   58m   v1.30.3
ci-ln-fm1qnwt-72292-99kt6-master-1         Ready                      master   58m   v1.30.3
ci-ln-fm1qnwt-72292-99kt6-master-2         Ready                      master   58m   v1.30.3
ci-ln-fm1qnwt-72292-99kt6-worker-a-h5gt4   Ready,SchedulingDisabled   worker   48m   v1.30.3
ci-ln-fm1qnwt-72292-99kt6-worker-b-7vtmd   Ready                      worker   48m   v1.30.3
ci-ln-fm1qnwt-72292-99kt6-worker-c-rhzkv   Ready                      worker   48m   v1.30.3

After a node returns to the Ready state, start a debug session for that node:
```
$ oc debug node/<node_name>
```
Set /host as the root directory within the debug shell:
```
sh-4.4# chroot /host
```
Check that the sys/fs/cgroup/cgroup2fs or sys/fs/cgroup/tmpfs file is present on your nodes:
```
$ stat -c %T -f /sys/fs/cgroup
```
Example output for cgroup v2
```
cgroup2fs
```
Example output for cgroup v1
```
tmpfs
```

Additional resources

OpenShift Container Platform installation overview