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Chapter 12. Nodes
12.1. Node maintenance Copia collegamentoCollegamento copiato negli appunti!
Nodes can be placed into maintenance mode by using the oc adm
utility or NodeMaintenance
custom resources (CRs).
The node-maintenance-operator
(NMO) is no longer shipped with OpenShift Virtualization. It is deployed as a standalone Operator from the OperatorHub in the Red Hat OpenShift Service on AWS web console or by using the OpenShift CLI (oc
).
For more information on remediation, fencing, and maintaining nodes, see the Workload Availability for Red Hat OpenShift documentation.
Virtual machines (VMs) must have a persistent volume claim (PVC) with a shared ReadWriteMany
(RWX) access mode to be live migrated.
The Node Maintenance Operator watches for new or deleted NodeMaintenance
CRs. When a new NodeMaintenance
CR is detected, no new workloads are scheduled and the node is cordoned off from the rest of the cluster. All pods that can be evicted are evicted from the node. When a NodeMaintenance
CR is deleted, the node that is referenced in the CR is made available for new workloads.
Using a NodeMaintenance
CR for node maintenance tasks achieves the same results as the oc adm cordon
and oc adm drain
commands using standard Red Hat OpenShift Service on AWS custom resource processing.
12.1.1. Eviction strategies Copia collegamentoCollegamento copiato negli appunti!
Placing a node into maintenance marks the node as unschedulable and drains all the VMs and pods from it.
You can configure eviction strategies for virtual machines (VMs) or for the cluster.
- VM eviction strategy
The VM
LiveMigrate
eviction strategy ensures that a virtual machine instance (VMI) is not interrupted if the node is placed into maintenance or drained. VMIs with this eviction strategy will be live migrated to another node.You can configure eviction strategies for virtual machines (VMs) by using the Red Hat OpenShift Service on AWS web console or the command line.
ImportantThe default eviction strategy is
LiveMigrate
. A non-migratable VM with aLiveMigrate
eviction strategy might prevent nodes from draining or block an infrastructure upgrade because the VM is not evicted from the node. This situation causes a migration to remain in aPending
orScheduling
state unless you shut down the VM manually.You must set the eviction strategy of non-migratable VMs to
LiveMigrateIfPossible
, which does not block an upgrade, or toNone
, for VMs that should not be migrated.
- Cluster eviction strategy
- You can configure an eviction strategy for the cluster to prioritize workload continuity or infrastructure upgrade.
Eviction strategy | Description | Interrupts workflow | Blocks upgrades |
---|---|---|---|
| Prioritizes workload continuity over upgrades. | No | Yes 2 |
| Prioritizes upgrades over workload continuity to ensure that the environment is updated. | Yes | No |
| Shuts down VMs with no eviction strategy. | Yes | No |
- Default eviction strategy for multi-node clusters.
- If a VM blocks an upgrade, you must shut down the VM manually.
- Default eviction strategy for single-node OpenShift.
12.1.1.1. Configuring a VM eviction strategy using the CLI Copia collegamentoCollegamento copiato negli appunti!
You can configure an eviction strategy for a virtual machine (VM) by using the command line.
The default eviction strategy is LiveMigrate
. A non-migratable VM with a LiveMigrate
eviction strategy might prevent nodes from draining or block an infrastructure upgrade because the VM is not evicted from the node. This situation causes a migration to remain in a Pending
or Scheduling
state unless you shut down the VM manually.
You must set the eviction strategy of non-migratable VMs to LiveMigrateIfPossible
, which does not block an upgrade, or to None
, for VMs that should not be migrated.
Prerequisites
-
You have installed the OpenShift CLI (
oc
).
Procedure
Edit the
VirtualMachine
resource by running the following command:oc edit vm <vm_name> -n <namespace>
$ oc edit vm <vm_name> -n <namespace>
Copy to Clipboard Copied! Toggle word wrap Toggle overflow Example eviction strategy
Copy to Clipboard Copied! Toggle word wrap Toggle overflow - 1
- Specify the eviction strategy. The default value is
LiveMigrate
.
Restart the VM to apply the changes:
virtctl restart <vm_name> -n <namespace>
$ virtctl restart <vm_name> -n <namespace>
Copy to Clipboard Copied! Toggle word wrap Toggle overflow
12.1.1.2. Configuring a cluster eviction strategy by using the CLI Copia collegamentoCollegamento copiato negli appunti!
You can configure an eviction strategy for a cluster by using the command line.
Prerequisites
-
You have installed the OpenShift CLI (
oc
).
Procedure
Edit the
hyperconverged
resource by running the following command:oc edit hyperconverged kubevirt-hyperconverged -n openshift-cnv
$ oc edit hyperconverged kubevirt-hyperconverged -n openshift-cnv
Copy to Clipboard Copied! Toggle word wrap Toggle overflow Set the cluster eviction strategy as shown in the following example:
Example cluster eviction strategy
Copy to Clipboard Copied! Toggle word wrap Toggle overflow
12.1.2. Run strategies Copia collegamentoCollegamento copiato negli appunti!
The spec.runStrategy
key determines how a VM behaves under certain conditions.
12.1.2.1. Run strategies Copia collegamentoCollegamento copiato negli appunti!
The spec.runStrategy
key has four possible values:
Always
- The virtual machine instance (VMI) is always present when a virtual machine (VM) is created on another node. A new VMI is created if the original stops for any reason.
RerunOnFailure
- The VMI is re-created on another node if the previous instance fails. The instance is not re-created if the VM stops successfully, such as when it is shut down.
Manual
-
You control the VMI state manually with the
start
,stop
, andrestart
virtctl client commands. The VM is not automatically restarted. Halted
- No VMI is present when a VM is created.
Different combinations of the virtctl start
, stop
and restart
commands affect the run strategy.
The following table describes a VM’s transition between states. The first column shows the VM’s initial run strategy. The remaining columns show a virtctl command and the new run strategy after that command is run.
Initial run strategy | Start | Stop | Restart |
---|---|---|---|
Always | - | Halted | Always |
RerunOnFailure | RerunOnFailure | RerunOnFailure | RerunOnFailure |
Manual | Manual | Manual | Manual |
Halted | Always | - | - |
If a node in a cluster installed by using installer-provisioned infrastructure fails the machine health check and is unavailable, VMs with runStrategy: Always
or runStrategy: RerunOnFailure
are rescheduled on a new node.
12.1.2.2. Configuring a VM run strategy by using the CLI Copia collegamentoCollegamento copiato negli appunti!
You can configure a run strategy for a virtual machine (VM) by using the command line.
Prerequisites
-
You have installed the OpenShift CLI (
oc
).
Procedure
Edit the
VirtualMachine
resource by running the following command:oc edit vm <vm_name> -n <namespace>
$ oc edit vm <vm_name> -n <namespace>
Copy to Clipboard Copied! Toggle word wrap Toggle overflow Example run strategy
apiVersion: kubevirt.io/v1 kind: VirtualMachine spec: runStrategy: Always # ...
apiVersion: kubevirt.io/v1 kind: VirtualMachine spec: runStrategy: Always # ...
Copy to Clipboard Copied! Toggle word wrap Toggle overflow
12.1.3. Maintaining bare metal nodes Copia collegamentoCollegamento copiato negli appunti!
When you deploy Red Hat OpenShift Service on AWS on bare metal infrastructure, there are additional considerations that must be taken into account compared to deploying on cloud infrastructure. Unlike in cloud environments where the cluster nodes are considered ephemeral, re-provisioning a bare metal node requires significantly more time and effort for maintenance tasks.
When a bare metal node fails, for example, if a fatal kernel error happens or a NIC card hardware failure occurs, workloads on the failed node need to be restarted elsewhere else on the cluster while the problem node is repaired or replaced. Node maintenance mode allows cluster administrators to gracefully power down nodes, moving workloads to other parts of the cluster and ensuring workloads do not get interrupted. Detailed progress and node status details are provided during maintenance.
12.2. Managing node labeling for obsolete CPU models Copia collegamentoCollegamento copiato negli appunti!
You can schedule a virtual machine (VM) on a node as long as the VM CPU model and policy are supported by the node.
12.2.1. About node labeling for obsolete CPU models Copia collegamentoCollegamento copiato negli appunti!
The OpenShift Virtualization Operator uses a predefined list of obsolete CPU models to ensure that a node supports only valid CPU models for scheduled VMs.
By default, the following CPU models are eliminated from the list of labels generated for the node:
Example 12.1. Obsolete CPU models
This predefined list is not visible in the HyperConverged
CR. You cannot remove CPU models from this list, but you can add to the list by editing the spec.obsoleteCPUs.cpuModels
field of the HyperConverged
CR.
12.2.2. Configuring obsolete CPU models Copia collegamentoCollegamento copiato negli appunti!
You can configure a list of obsolete CPU models by editing the HyperConverged
custom resource (CR).
Procedure
Edit the
HyperConverged
custom resource, specifying the obsolete CPU models in theobsoleteCPUs
array. For example:Copy to Clipboard Copied! Toggle word wrap Toggle overflow - 1
- Replace the example values in the
cpuModels
array with obsolete CPU models. Any value that you specify is added to a predefined list of obsolete CPU models. The predefined list is not visible in the CR.
12.3. Preventing node reconciliation Copia collegamentoCollegamento copiato negli appunti!
Use skip-node
annotation to prevent the node-labeller
from reconciling a node.
12.3.1. Using skip-node annotation Copia collegamentoCollegamento copiato negli appunti!
If you want the node-labeller
to skip a node, annotate that node by using the oc
CLI.
Prerequisites
-
You have installed the OpenShift CLI (
oc
).
Procedure
Annotate the node that you want to skip by running the following command:
oc annotate node <node_name> node-labeller.kubevirt.io/skip-node=true
$ oc annotate node <node_name> node-labeller.kubevirt.io/skip-node=true
1 Copy to Clipboard Copied! Toggle word wrap Toggle overflow - 1
- Replace
<node_name>
with the name of the relevant node to skip.
Reconciliation resumes on the next cycle after the node annotation is removed or set to false.