1. Documentation
×

Working with nodes

Understanding how to evacuate pods on nodes

Evacuating pods allows you to migrate all or selected pods from a given node or nodes.

You can only evacuate pods backed by a replication controller. The replication controller creates new pods on other nodes and removes the existing pods from the specified node(s).

Bare pods, meaning those not backed by a replication controller, are unaffected by default. You can evacuate a subset of pods by specifying a pod-selector. Pod selectors are based on labels, so all the pods with the specified label will be evacuated.

Procedure

  1. Mark the nodes unschedulable before performing the pod evacuation.

    1. Mark the node as unschedulable:

      $ oc adm cordon <node1>
      Example output
      node/<node1> cordoned

    2. Check that the node status is NotReady,SchedulingDisabled:

      $ oc get node <node1>
      Example output
      NAME        STATUS                        ROLES     AGE       VERSION
<node1>     NotReady,SchedulingDisabled   worker    1d        v1.23.0

  2. Evacuate the pods using one of the following methods:

    • Evacuate all or selected pods on one or more nodes:

      $ oc adm drain <node1> <node2> [--pod-selector=<pod_selector>]

    • Force the deletion of bare pods using the --force option. When set to true, deletion continues even if there are pods not managed by a replication controller, replica set, job, daemon set, or stateful set:

      $ oc adm drain <node1> <node2> --force=true

    • Set a period of time in seconds for each pod to terminate gracefully, use --grace-period. If negative, the default value specified in the pod will be used:

      $ oc adm drain <node1> <node2> --grace-period=-1

    • Ignore pods managed by daemon sets using the --ignore-daemonsets flag set to true:

      $ oc adm drain <node1> <node2> --ignore-daemonsets=true

    • Set the length of time to wait before giving up using the --timeout flag. A value of 0 sets an infinite length of time:

      $ oc adm drain <node1> <node2> --timeout=5s

    • Delete pods even if there are pods using emptyDir using the --delete-local-data flag set to true. Local data is deleted when the node is drained:

      $ oc adm drain <node1> <node2> --delete-local-data=true

    • List objects that will be migrated without actually performing the evacuation, using the --dry-run option set to true:

      $ oc adm drain <node1> <node2>  --dry-run=true

      Instead of specifying specific node names (for example, <node1> <node2>), you can use the --selector=<node_selector> option to evacuate pods on selected nodes.

  3. Mark the node as schedulable when done.

    $ oc adm uncordon <node1>

Understanding how to update labels on nodes

You can update any label on a node.

Node labels are not persisted after a node is deleted even if the node is backed up by a Machine.

Any change to a MachineSet object is not applied to existing machines owned by the machine set. For example, labels edited or added to an existing MachineSet object are not propagated to existing machines and nodes associated with the machine set.

  • The following command adds or updates labels on a node:

    $ oc label node <node> <key_1>=<value_1> ... <key_n>=<value_n>

    For example:

    $ oc label nodes webconsole-7f7f6 unhealthy=true

    You can alternatively apply the following YAML to apply the label:

    kind: Node
apiVersion: v1
metadata:
  name: webconsole-7f7f6
  labels:
    unhealthy: 'true'

  • The following command updates all pods in the namespace:

    $ oc label pods --all <key_1>=<value_1>

    For example:

    $ oc label pods --all status=unhealthy

Understanding how to mark nodes as unschedulable or schedulable

By default, healthy nodes with a Ready status are marked as schedulable, which means that you can place new pods on the node. Manually marking a node as unschedulable blocks any new pods from being scheduled on the node. Existing pods on the node are not affected.

  • The following command marks a node or nodes as unschedulable:

    Example output
    $ oc adm cordon <node>

    For example:

    $ oc adm cordon node1.example.com
    Example output
    node/node1.example.com cordoned

NAME                 LABELS                                        STATUS
node1.example.com    kubernetes.io/hostname=node1.example.com      Ready,SchedulingDisabled

  • The following command marks a currently unschedulable node or nodes as schedulable:

    $ oc adm uncordon <node1>

    Alternatively, instead of specifying specific node names (for example, <node>), you can use the --selector=<node_selector> option to mark selected nodes as schedulable or unschedulable.

Configuring control plane nodes as schedulable

You can configure control plane nodes to be schedulable, meaning that new pods are allowed for placement on the master nodes. By default, control plane nodes are not schedulable.

You can set the masters to be schedulable, but must retain the worker nodes.

You can deploy OKD with no worker nodes on a bare metal cluster. In this case, the control plane nodes are marked schedulable by default.

You can allow or disallow control plane nodes to be schedulable by configuring the mastersSchedulable field.

When you configure control plane nodes from the default unschedulable to schedulable, additional subscriptions are required. This is because control plane nodes then become worker nodes.
Procedure

  1. Edit the schedulers.config.openshift.io resource.

    $ oc edit schedulers.config.openshift.io cluster

  2. Configure the mastersSchedulable field.

    apiVersion: config.openshift.io/v1
kind: Scheduler
metadata:
  creationTimestamp: "2019-09-10T03:04:05Z"
  generation: 1
  name: cluster
  resourceVersion: "433"
  selfLink: /apis/config.openshift.io/v1/schedulers/cluster
  uid: a636d30a-d377-11e9-88d4-0a60097bee62
spec:
  mastersSchedulable: false (1)
status: {}
    1 Set to true to allow control plane nodes to be schedulable, or false to disallow control plane nodes to be schedulable.

  3. Save the file to apply the changes.

Deleting nodes

Deleting nodes from a cluster

When you delete a node using the CLI, the node object is deleted in Kubernetes, but the pods that exist on the node are not deleted. Any bare pods not backed by a replication controller become inaccessible to OKD. Pods backed by replication controllers are rescheduled to other available nodes. You must delete local manifest pods.

Procedure

To delete a node from the OKD cluster, edit the appropriate MachineSet object:

If you are running cluster on bare metal, you cannot delete a node by editing MachineSet objects. Machine sets are only available when a cluster is integrated with a cloud provider. Instead you must unschedule and drain the node before manually deleting it.

  1. View the machine sets that are in the cluster:

    $ oc get machinesets -n openshift-machine-api

    The machine sets are listed in the form of <clusterid>-worker-<aws-region-az>.

  2. Scale the machine set:

    $ oc scale --replicas=2 machineset <machineset> -n openshift-machine-api

    Or:

    $ oc edit machineset <machineset> -n openshift-machine-api

    You can alternatively apply the following YAML to scale the machine set:

    apiVersion: machine.openshift.io/v1beta1
kind: MachineSet
metadata:
  name: <machineset>
  namespace: openshift-machine-api
spec:
  replicas: 2
Additional resources

Deleting nodes from a bare metal cluster

When you delete a node using the CLI, the node object is deleted in Kubernetes, but the pods that exist on the node are not deleted. Any bare pods not backed by a replication controller become inaccessible to OKD. Pods backed by replication controllers are rescheduled to other available nodes. You must delete local manifest pods.

Procedure

Delete a node from an OKD cluster running on bare metal by completing the following steps:

  1. Mark the node as unschedulable:

    $ oc adm cordon <node_name>

  2. Drain all pods on the node:

    $ oc adm drain <node_name> --force=true

    This step might fail if the node is offline or unresponsive. Even if the node does not respond, it might still be running a workload that writes to shared storage. To avoid data corruption, power down the physical hardware before you proceed.

  3. Delete the node from the cluster:

    $ oc delete node <node_name>

    Although the node object is now deleted from the cluster, it can still rejoin the cluster after reboot or if the kubelet service is restarted. To permanently delete the node and all its data, you must decommission the node.

  4. If you powered down the physical hardware, turn it back on so that the node can rejoin the cluster.

Setting SELinux booleans

OKD allows you to enable and disable an SELinux boolean on a Fedora CoreOS (FCOS) node. The following procedure explains how to modify SELinux booleans on nodes using the Machine Config Operator (MCO). This procedure uses container_manage_cgroup as the example boolean. You can modify this value to whichever boolean you need.

Prerequisites

  • You have installed the OpenShift CLI (oc).

Procedure

  1. Create a new YAML file with a MachineConfig object, displayed in the following example:

    apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: worker
  name: 99-worker-setsebool
spec:
  config:
    ignition:
      version: 2.2.0
    systemd:
      units:
      - contents: |
          [Unit]
          Description=Set SELinux booleans
          Before=kubelet.service

          [Service]
          Type=oneshot
          ExecStart=/sbin/setsebool container_manage_cgroup=on
          RemainAfterExit=true

          [Install]
          WantedBy=multi-user.target graphical.target
        enabled: true
        name: setsebool.service

  2. Create the new MachineConfig object by running the following command:

    $ oc create -f 99-worker-setsebool.yaml

Applying any changes to the MachineConfig object causes all affected nodes to gracefully reboot after the change is applied.

Adding kernel arguments to nodes

In some special cases, you might want to add kernel arguments to a set of nodes in your cluster. This should only be done with caution and clear understanding of the implications of the arguments you set.

Improper use of kernel arguments can result in your systems becoming unbootable.

Examples of kernel arguments you could set include:

  • enforcing=0: Configures Security Enhanced Linux (SELinux) to run in permissive mode. In permissive mode, the system acts as if SELinux is enforcing the loaded security policy, including labeling objects and emitting access denial entries in the logs, but it does not actually deny any operations. While not recommended for production systems, permissive mode can be helpful for debugging.

  • nosmt: Disables symmetric multithreading (SMT) in the kernel. Multithreading allows multiple logical threads for each CPU. You could consider nosmt in multi-tenant environments to reduce risks from potential cross-thread attacks. By disabling SMT, you essentially choose security over performance.

  • systemd.unified_cgroup_hierarchy: Enables Linux control groups version 2 (cgroups v2). Cgroup v2 is the next version of the kernel control groups and offers multiple improvements.

See Kernel.org kernel parameters for a list and descriptions of kernel arguments.

In the following procedure, you create a MachineConfig object that identifies:

  • A set of machines to which you want to add the kernel argument. In this case, machines with a worker role.

  • Kernel arguments that are appended to the end of the existing kernel arguments.

  • A label that indicates where in the list of machine configs the change is applied.

Prerequisites

  • Have administrative privilege to a working OKD cluster.

Procedure

  1. List existing MachineConfig objects for your OKD cluster to determine how to label your machine config:

    $ oc get MachineConfig
    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
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-23e785de7587df95a4b517e0647e5ab7   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
rendered-worker-5d596d9293ca3ea80c896a1191735bb1   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m

  2. Create a MachineConfig object file that identifies the kernel argument (for example, 05-worker-kernelarg-selinuxpermissive.yaml)

    apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: worker(1)
  name: 05-worker-kernelarg-selinuxpermissive(2)
spec:
  config:
    ignition:
      version: 3.2.0
  kernelArguments:
    - enforcing=0(3)
    1 Applies the new kernel argument only to worker nodes.
    2 Named to identify where it fits among the machine configs (05) and what it does (adds a kernel argument to configure SELinux permissive mode).
    3 Identifies the exact kernel argument as enforcing=0.

  3. Create the new machine config:

    $ oc create -f 05-worker-kernelarg-selinuxpermissive.yaml

  4. Check the machine configs to see that the new one was added:

    $ oc get MachineConfig
    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
05-worker-kernelarg-selinuxpermissive                                                         3.2.0             105s
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-23e785de7587df95a4b517e0647e5ab7   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
rendered-worker-5d596d9293ca3ea80c896a1191735bb1   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m

  5. Check the nodes:

    $ oc get nodes
    Example output
    NAME                           STATUS                     ROLES    AGE   VERSION
ip-10-0-136-161.ec2.internal   Ready                      worker   28m   v1.23.0
ip-10-0-136-243.ec2.internal   Ready                      master   34m   v1.23.0
ip-10-0-141-105.ec2.internal   Ready,SchedulingDisabled   worker   28m   v1.23.0
ip-10-0-142-249.ec2.internal   Ready                      master   34m   v1.23.0
ip-10-0-153-11.ec2.internal    Ready                      worker   28m   v1.23.0
ip-10-0-153-150.ec2.internal   Ready                      master   34m   v1.23.0

    You can see that scheduling on each worker node is disabled as the change is being applied.

  6. Check that the kernel argument worked by going to one of the worker nodes and listing the kernel command line arguments (in /proc/cmdline on the host):

    $ oc debug node/ip-10-0-141-105.ec2.internal
    Example output
    Starting pod/ip-10-0-141-105ec2internal-debug ...
To use host binaries, run `chroot /host`

sh-4.2# cat /host/proc/cmdline
BOOT_IMAGE=/ostree/rhcos-... console=tty0 console=ttyS0,115200n8
rootflags=defaults,prjquota rw root=UUID=fd0... ostree=/ostree/boot.0/rhcos/16...
coreos.oem.id=qemu coreos.oem.id=ec2 ignition.platform.id=ec2 enforcing=0

sh-4.2# exit

    You should see the enforcing=0 argument added to the other kernel arguments.

Enabling Linux control groups version 2 (cgroups v2)

You can enable Linux control groups version 2 (cgroups v2) on specific nodes in your cluster by using a machine config. The OKD process for enabling cgroups v2 disables all cgroups version 1 controllers and hierarchies.

The OKD cgroups version 2 feature is in Developer Preview and is not supported by Red Hat at this time.
Prerequisites

  • You have a running OKD cluster that uses version 4.10 or later.

  • You are logged in to the cluster as a user with administrative privileges.

  • You have the node-role.kubernetes.io value for the node(s) you want to configure.

    $ oc describe node <node-name>
    Example output
    Name:               ci-ln-v05w5m2-72292-5s9ht-worker-a-r6fpg
Roles:              worker
Labels:             beta.kubernetes.io/arch=amd64
                    beta.kubernetes.io/instance-type=n1-standard-4
                    beta.kubernetes.io/os=linux
                    failure-domain.beta.kubernetes.io/region=us-central1
                    failure-domain.beta.kubernetes.io/zone=us-central1-a
                    kubernetes.io/arch=amd64
                    kubernetes.io/hostname=ci-ln-v05w5m2-72292-5s9ht-worker-a-r6fpg
                    kubernetes.io/os=linux
                    node-role.kubernetes.io/worker= (1)
#...
    1 This value is the node role you need.
Procedure

  1. Enable cgroups v2 on nodes:

    • Create a machine config file YAML, such as worker-cgroups-v2.yaml:

      apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: "worker" (1)
  name: worker-enable-cgroups-v2
spec:
  kernelArguments:
    - systemd.unified_cgroup_hierarchy=1 (2)
    - cgroup_no_v1="all" (3)
      1 Specifies the node-role.kubernetes.io value for the nodes you want to configure, such as master, worker, or infra.
      2 Enables cgroups v2 in systemd.
      3 Disables cgroups v1.

    • Create the new machine config:

      $ oc create -f worker-enable-cgroups-v2.yaml

  2. Check the machine configs to see that the new one was added:

    $ oc get MachineConfig
    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
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-23e785de7587df95a4b517e0647e5ab7   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
rendered-worker-5d596d9293ca3ea80c896a1191735bb1   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
worker-enable-cgroups-v2                                                                      3.2.0             10s

  3. Check the nodes to see that scheduling on each affected node 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                      master   58m   v1.23.0
ci-ln-fm1qnwt-72292-99kt6-master-1         Ready                      master   58m   v1.23.0
ci-ln-fm1qnwt-72292-99kt6-master-2         Ready                      master   58m   v1.23.0
ci-ln-fm1qnwt-72292-99kt6-worker-a-h5gt4   Ready,SchedulingDisabled   worker   48m   v1.23.0
ci-ln-fm1qnwt-72292-99kt6-worker-b-7vtmd   Ready                      worker   48m   v1.23.0
ci-ln-fm1qnwt-72292-99kt6-worker-c-rhzkv   Ready                      worker   48m   v1.23.0

  4. After a node returns to the Ready state, you can verify that cgroups v2 is enabled by checking that the sys/fs/cgroup/cgroup.controllers file is present on the node. This file is created by cgroups v2.

    • Start a debug session for that node:

      $ oc debug node/<node_name>

    • Locate the sys/fs/cgroup/cgroup.controllers file. If this file is present, cgroups v2 is enabled on that node.

      Example output
      cgroup.controllers	cgroup.stat		cpuset.cpus.effective  io.stat		pids
cgroup.max.depth	cgroup.subtree_control	cpuset.mems.effective  kubepods.slice	system.slice
cgroup.max.descendants	cgroup.threads		init.scope	       memory.pressure	user.slice
cgroup.procs		cpu.pressure		io.pressure	       memory.stat
Additional resources

  • For information about enabling cgroups v2 during installation, see the Optional parameters table in the Installation configuration parameters section of your installation process.

Enabling swap memory use on nodes

Enabling swap memory use on nodes is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview/.

You can enable swap memory use for OKD workloads on a per-node basis.

Enabling swap memory can negatively impact workload performance and out-of-resource handling. Do not enable swap memory on master nodes.

To enable swap memory, create a kubeletconfig custom resource (CR) to set the swapbehavior parameter. You can set limited or unlimited swap memory:

  • Limited: Use the LimitedSwap value to limit how much swap memory workloads can use. Any workloads on the node that are not managed by OKD can still use swap memory. The LimitedSwap behavior depends on whether the node is running with Linux control groups version 1 (cgroups v1) or version 2 (cgroups v2):

    • cgroups v1: OKD workloads can use any combination of memory and swap, up to the pod’s memory limit, if set.

    • cgroups v2: OKD workloads cannot use swap memory.

  • Unlimited: Use the UnlimitedSwap value to allow workloads to use as much swap memory as they request, up to the system limit.

Because the kubelet will not start in the presence of swap memory without this configuration, you must enable swap memory in OKD before enabling swap memory on the nodes. If there is no swap memory present on a node, enabling swap memory in OKD has no effect.

Prerequisites

  • You have a running OKD cluster that uses version 4.10 or later.

  • You are logged in to the cluster as a user with administrative privileges.

  • You have enabled the TechPreviewNoUpgrade feature set on the cluster (see Nodes → Enabling features using feature gates).

    Enabling the TechPreviewNoUpgrade feature set cannot be undone and prevents minor version updates. These feature sets are not recommended on production clusters.

  • If cgroups v2 is enabled on a node, you must enable swap accounting on the node, by setting the swapaccount=1 kernel argument.

Procedure

  1. Apply a custom label to the machine config pool where you want to allow swap memory.

    $ oc label machineconfigpool worker kubelet-swap=enabled

  2. Create a custom resource (CR) to enable and configure swap settings.

    apiVersion: machineconfiguration.openshift.io/v1
kind: KubeletConfig
metadata:
  name: swap-config
spec:
  machineConfigPoolSelector:
    matchLabels:
      kubelet-swap: enabled
  kubeletConfig:
    failSwapOn: false (1)
    memorySwap:
      swapBehavior: LimitedSwap (2)
    1 Set to false to enable swap memory use on the associated nodes. Set to true to disable swap memory use.
    2 Specify the swap memory behavior. If unspecified, the default is LimitedSwap.

  3. Enable swap memory on the machines.

Migrating control plane nodes from one RHOSP host to another

You can run a script that moves a control plane node from one OpenStack node to another.

Prerequisites

  • The environment variable OS_CLOUD refers to a clouds entry that has administrative credentials in a clouds.yaml file.

  • The environment variable KUBECONFIG refers to a configuration that contains administrative OKD credentials.

Procedure

  • From a command line, run the following script:

#!/usr/bin/env bash

set -Eeuo pipefail

if [ $# -lt 1 ]; then
	echo "Usage: '$0 node_name'"
	exit 64
fi

# Check for admin OpenStack credentials
openstack server list --all-projects >/dev/null || { >&2 echo "The script needs OpenStack admin credentials. Exiting"; exit 77; }

# Check for admin OpenShift credentials
oc adm top node >/dev/null || { >&2 echo "The script needs OpenShift admin credentials. Exiting"; exit 77; }

set -x

declare -r node_name="$1"
declare server_id
server_id="$(openstack server list --all-projects -f value -c ID -c Name | grep "$node_name" | cut -d' ' -f1)"
readonly server_id

# Drain the node
oc adm cordon "$node_name"
oc adm drain "$node_name" --delete-emptydir-data --ignore-daemonsets --force

# Power off the server
oc debug "node/${node_name}" -- chroot /host shutdown -h 1

# Verify the server is shut off
until openstack server show "$server_id" -f value -c status | grep -q 'SHUTOFF'; do sleep 5; done

# Migrate the node
openstack server migrate --wait "$server_id"

# Resize the VM
openstack server resize confirm "$server_id"

# Wait for the resize confirm to finish
until openstack server show "$server_id" -f value -c status | grep -q 'SHUTOFF'; do sleep 5; done

# Restart the VM
openstack server start "$server_id"

# Wait for the node to show up as Ready:
until oc get node "$node_name" | grep -q "^${node_name}[[:space:]]\+Ready"; do sleep 5; done

# Uncordon the node
oc adm uncordon "$node_name"

# Wait for cluster operators to stabilize
until oc get co -o go-template='statuses: {{ range .items }}{{ range .status.conditions }}{{ if eq .type "Degraded" }}{{ if ne .status "False" }}DEGRADED{{ end }}{{ else if eq .type "Progressing"}}{{ if ne .status "False" }}PROGRESSING{{ end }}{{ else if eq .type "Available"}}{{ if ne .status "True" }}NOTAVAILABLE{{ end }}{{ end }}{{ end }}{{ end }}' | grep -qv '\(DEGRADED\|PROGRESSING\|NOTAVAILABLE\)'; do sleep 5; done

If the script completes, the control plane machine is migrated to a new OpenStack node.