OpenShift Container Platform

Manually allocating resources for nodes

As an administrator, you can manually set system-reserved CPU and memory resources for your nodes. Setting these values ensures that your cluster is running efficiently and prevents node failure due to resource starvation of system components.

By default, OpenShift Container Platform uses a script on each worker node to automatically determine the optimal system-reserved CPU and memory resources for nodes associated with a specific machine config pool and update the nodes with those values. The script runs on node start up.

If you updated your cluster from a version earlier than 4.21, automatic allocation of system resources is disabled by default. To enable the feature, delete the 50-worker-auto-sizing-disabled machine config.

However, you can manually set these values by using a KubeletConfig custom resource (CR) that includes a set of <resource_type>=<resource_quantity> pairs (for example, cpu=200m,memory=512Mi). You must use the spec.autoSizingReserved: false parameter in the KubeletConfig CR to override the default OpenShift Container Platform behavior of automatically setting the systemReserved values.

For memory and ephemeral-storage, you specify the resource quantity in units of bytes, such as 200Ki, 50Mi, or 5Gi. By default, the system-reserved CPU is 500m and system-reserved memory is 1Gi. For the cpu type, you specify the resource quantity in units of cores, such as 200m, 0.5, or 1. Note that 1000 millicores is equal to 1CPU/vCPU.

For details on the recommended system-reserved values, refer to the recommended system-reserved values.
To manually set resource values, you must use a kubelet configuration. You cannot use a machine config.

Prerequisites

Obtain the label associated with the static MachineConfigPool CRD for the type of node you want to configure by entering the following command:

Procedure

Create a custom resource (CR) for your configuration change.
Sample configuration for a resource allocation CR
```
apiVersion: machineconfiguration.openshift.io/v1
kind: KubeletConfig
metadata:
  name: set-allocatable
spec:
  autoSizingReserved: false
  machineConfigPoolSelector:
    matchLabels:
      pools.operator.machineconfiguration.openshift.io/worker: ""
  kubeletConfig:
    systemReserved:
      cpu: 1000m
      memory: 4Gi
      ephemeral-storage: 50Mi
#...
```
metadata.name

Specifies a name for the CR.

spec.autoSizingReserved

Specify false to override the default OpenShift Container Platform behavior of automatically setting the systemReserved values.

spec.machineConfigPoolSelector.matchLabels

Specifies a label from the machine config pool.

spec.kubeletConfig.systemReserved

Specifies the resources to reserve for the node components and system components.
Run the following command to create the CR:
```
$ oc create -f <file_name>.yaml
```

Verification

Log in to a node you configured by entering the following command:
```
$ oc debug node/<node_name>
```
Set /host as the root directory within the debug shell:
```
# chroot /host
```
View the /etc/node-sizing.env file:
Example output
```
SYSTEM_RESERVED_MEMORY=4Gi
SYSTEM_RESERVED_CPU=1000m
SYSTEM_RESERVED_ES=50Mi
```
The kubelet uses the system-reserved values in the /etc/node-sizing.env file.