Red Hat Summit13장. Nodes
13.1. Node maintenance
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 OpenShift Container Platform 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 OpenShift Container Platform custom resource processing.
13.1.1. Eviction strategies
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
LiveMigrateeviction 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 OpenShift Container Platform web console or the command line.
중요The default eviction strategy is
LiveMigrate. A non-migratable VM with aLiveMigrateeviction 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 aPendingorSchedulingstate 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.
13.1.1.1. Configuring a VM eviction strategy using the CLI
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
VirtualMachineresource by running the following command:$ oc edit vm <vm_name> -n <namespace>Example eviction strategy
apiVersion: kubevirt.io/v1 kind: VirtualMachine metadata: name: <vm_name> spec: template: spec: evictionStrategy: LiveMigrateIfPossible1 # ...- 1
- Specify the eviction strategy. The default value is
LiveMigrate.
Restart the VM to apply the changes:
$ virtctl restart <vm_name> -n <namespace>
13.1.1.2. Configuring a cluster eviction strategy by using the CLI
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
hyperconvergedresource by running the following command:$ oc edit hyperconverged kubevirt-hyperconverged -n openshift-cnvSet the cluster eviction strategy as shown in the following example:
Example cluster eviction strategy
apiVersion: hco.kubevirt.io/v1beta1 kind: HyperConverged metadata: name: kubevirt-hyperconverged spec: evictionStrategy: LiveMigrate # ...
13.1.2. Run strategies
The spec.runStrategy key determines how a VM behaves under certain conditions.
13.1.2.1. Run strategies
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.
RerunOnFailureThe 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.
중요Setting
spec.runStrategy: RerunOnFailureis an explicit command to start the VM. If the VM is intentionally stopped and you do not want it to start, do not change the run strategy value toRerunOnFailure.Manual-
You control the VMI state manually with the
start,stop, andrestartvirtctl 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.
13.1.2.2. Configuring a VM run strategy by using the CLI
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
VirtualMachineresource by running the following command:$ oc edit vm <vm_name> -n <namespace>Example run strategy
apiVersion: kubevirt.io/v1 kind: VirtualMachine spec: runStrategy: Always # ...
13.1.3. Maintaining bare metal nodes
When you deploy OpenShift Container Platform 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.
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