Chapter 10. Node maintenance

10.1. About node maintenance

10.1.1. Understanding node maintenance mode

Nodes can be placed into maintenance mode using the oc adm utility, or using NodeMaintenance custom resources (CRs).

Placing a node into maintenance marks the node as unschedulable and drains all the virtual machines and pods from it. Virtual machine instances that have a LiveMigrate eviction strategy are live migrated to another node without loss of service. This eviction strategy is configured by default in virtual machine created from common templates but must be configured manually for custom virtual machines.

Virtual machine instances without an eviction strategy are shut down. Virtual machines with a RunStrategy of Running or RerunOnFailure are recreated on another node. Virtual machines with a RunStrategy of Manual are not automatically restarted.

Important

Virtual machines must have a persistent volume claim (PVC) with a shared ReadWriteMany (RWX) access mode to be live migrated.

When installed as part of OpenShift Virtualization, 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.

Note

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.

10.1.2. 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.

Additional resources:

10.2. Setting a node to maintenance mode

Place a node into maintenance from the web console, CLI, or using a NodeMaintenance custom resource.

10.2.1. Setting a node to maintenance mode in the web console

Set a node to maintenance mode using the Options menu kebab found on each node in the Compute → Nodes list, or using the Actions control of the Node Details screen.

Procedure

  1. In the OpenShift Virtualization console, click Compute → Nodes.

  2. You can set the node to maintenance from this screen, which makes it easier to perform actions on multiple nodes in the one screen or from the Node Details screen where you can view comprehensive details of the selected node:

    • Click the Options menu kebab at the end of the node and select Start Maintenance.
    • Click the node name to open the Node Details screen and click Actions → Start Maintenance.
  3. Click Start Maintenance in the confirmation window.

The node will live migrate virtual machine instances that have the LiveMigration eviction strategy, and the node is no longer schedulable. All other pods and virtual machines on the node are deleted and recreated on another node.

10.2.2. Setting a node to maintenance mode in the CLI

Set a node to maintenance mode by marking it as unschedulable and using the oc adm drain command to evict or delete pods from the node.

Procedure

  1. Mark the node as unschedulable. The node status changes to NotReady,SchedulingDisabled. 

    $ oc adm cordon <node1>

  2. Drain the node in preparation for maintenance. The node live migrates virtual machine instances that have the LiveMigratable condition set to True and the spec:evictionStrategy field set to LiveMigrate. All other pods and virtual machines on the node are deleted and recreated on another node. 

    $ oc adm drain <node1> --delete-emptydir-data --ignore-daemonsets=true --force
    • The --delete-emptydir-data flag removes any virtual machine instances on the node that use emptyDir volumes. Data in these volumes is ephemeral and is safe to be deleted after termination.
    • The --ignore-daemonsets=true flag ensures that daemon sets are ignored and pod eviction can continue successfully.
    • The --force flag is required to delete pods that are not managed by a replica set or daemon set controller.

10.2.3. Setting a node to maintenance mode with a NodeMaintenance custom resource

You can put a node into maintenance mode with a NodeMaintenance custom resource (CR). When you apply a NodeMaintenance CR, all allowed pods are evicted and the node is shut down. Evicted pods are queued to be moved to another node in the cluster.

Prerequisites

  • Install the OpenShift Container Platform CLI oc.
  • Log in to the cluster as a user with cluster-admin privileges.

Procedure

  1. Create the following node maintenance CR, and save the file as nodemaintenance-cr.yaml: 

    apiVersion: nodemaintenance.kubevirt.io/v1beta1
kind: NodeMaintenance
metadata:
  name: maintenance-example  1
spec:
  nodeName: node-1.example.com 2
  reason: "Node maintenance" 3
    1
    Node maintenance CR name
    2
    The name of the node to be put into maintenance mode
    3
    Plain text description of the reason for maintenance

  2. Apply the node maintenance schedule by running the following command: 

    $ oc apply -f nodemaintenance-cr.yaml

  3. Check the progress of the maintenance task by running the following command, replacing <node-name> with the name of your node: 

    $ oc describe node <node-name>

    Example output

    Events:
  Type     Reason                     Age                   From     Message
  ----     ------                     ----                  ----     -------
  Normal   NodeNotSchedulable         61m                   kubelet  Node node-1.example.com status is now: NodeNotSchedulable

10.2.3.1. Checking status of current NodeMaintenance CR tasks

You can check the status of current NodeMaintenance CR tasks.

Prerequisites

  • Install the OpenShift Container Platform CLI oc.
  • Log in as a user with cluster-admin privileges.

Procedure

  • Check the status of current node maintenance tasks by running the following command: 

    $ oc get NodeMaintenance -o yaml

    Example output

    apiVersion: v1
items:
- apiVersion: nodemaintenance.kubevirt.io/v1beta1
  kind: NodeMaintenance
  metadata:
...
  spec:
    nodeName: node-1.example.com
    reason: Node maintenance
  status:
    evictionPods: 3   1
    pendingPods:
    - pod-example-workload-0
    - httpd
    - httpd-manual
    phase: Running
    lastError: "Last failure message" 2
    totalpods: 5
...

    1
    evictionPods is the number of pods scheduled for eviction.
    2
    lastError records the latest eviction error, if any.

Additional resources:

10.3. Resuming a node from maintenance mode

Resuming a node brings it out of maintenance mode and makes it schedulable again.

Resume a node from maintenance mode from the web console, CLI, or by deleting the NodeMaintenance custom resource.

10.3.1. Resuming a node from maintenance mode in the web console

Resume a node from maintenance mode using the Options menu kebab found on each node in the Compute → Nodes list, or using the Actions control of the Node Details screen.

Procedure

  1. In the OpenShift Virtualization console, click Compute → Nodes.

  2. You can resume the node from this screen, which makes it easier to perform actions on multiple nodes in the one screen, or from the Node Details screen where you can view comprehensive details of the selected node:

    • Click the Options menu kebab at the end of the node and select Stop Maintenance.
    • Click the node name to open the Node Details screen and click Actions → Stop Maintenance.
  3. Click Stop Maintenance in the confirmation window.

The node becomes schedulable, but virtual machine instances that were running on the node prior to maintenance will not automatically migrate back to this node.

10.3.2. Resuming a node from maintenance mode in the CLI

Resume a node from maintenance mode by making it schedulable again.

Procedure

  • Mark the node as schedulable. You can then resume scheduling new workloads on the node. 

    $ oc adm uncordon <node1>

10.3.3. Resuming a node from maintenance mode that was initiated with a NodeMaintenance CR

You can resume a node by deleting the NodeMaintenance CR.

Prerequisites

  • Install the OpenShift Container Platform CLI oc.
  • Log in to the cluster as a user with cluster-admin privileges.

Procedure

  • When your node maintenance task is complete, delete the active NodeMaintenance CR: 

    $ oc delete -f nodemaintenance-cr.yaml

    Example output

    nodemaintenance.nodemaintenance.kubevirt.io "maintenance-example" deleted

10.4. Automatic renewal of TLS certificates

All TLS certificates for OpenShift Virtualization components are renewed and rotated automatically. You are not required to refresh them manually.

10.4.1. TLS certificates automatic renewal schedules

TLS certificates are automatically deleted and replaced according to the following schedule:

  • KubeVirt certificates are renewed daily.
  • Containerized Data Importer controller (CDI) certificates are renewed every 15 days.
  • MAC pool certificates are renewed every year.

Automatic TLS certificate rotation does not disrupt any operations. For example, the following operations continue to function without any disruption:

  • Migrations
  • Image uploads
  • VNC and console connections

10.5. Managing node labeling for obsolete CPU models

You can schedule a virtual machine (VM) on a node where the CPU model and policy attribute of the VM are compatible with the CPU models and policy attributes that the node supports. By specifying a list of obsolete CPU models in a config map, you can exclude them from the list of labels created for CPU models.

10.5.1. Understanding node labeling for obsolete CPU models

To ensure that a node supports only valid CPU models for scheduled VMs, create a config map with a list of obsolete CPU models. When the node-labeller obtains the list of obsolete CPU models, it eliminates those CPU models and creates labels for valid CPU models.

Note

If you do not configure a config map with a list of obsolete CPU models, all CPU models are evaluated for labels, including obsolete CPU models that are not present in your environment.

Through the process of iteration, the list of base CPU features in the minimum CPU model are eliminated from the list of labels generated for the node. For example, an environment might have two supported CPU models: Penryn and Haswell.

If Penryn is specified as the CPU model for minCPU, the node-labeller evaluates each base CPU feature for Penryn and compares it with each CPU feature supported by Haswell. If the CPU feature is supported by both Penryn and Haswell, the node-labeller eliminates that feature from the list of CPU features for creating labels. If a CPU feature is supported only by Haswell and not by Penryn, that CPU feature is included in the list of generated labels. The node-labeller follows this iterative process to eliminate base CPU features that are present in the minimum CPU model and create labels.

The following example shows the complete list of CPU features for Penryn which is specified as the CPU model for minCPU:

Example of CPU features for Penryn

apic
clflush
cmov
cx16
cx8
de
fpu
fxsr
lahf_lm
lm
mca
mce
mmx
msr
mtrr
nx
pae
pat
pge
pni
pse
pse36
sep
sse
sse2
sse4.1
ssse3
syscall
tsc

The following example shows the complete list of CPU features for Haswell:

Example of CPU features for Haswell

aes
apic
avx
avx2
bmi1
bmi2
clflush
cmov
cx16
cx8
de
erms
fma
fpu
fsgsbase
fxsr
hle
invpcid
lahf_lm
lm
mca
mce
mmx
movbe
msr
mtrr
nx
pae
pat
pcid
pclmuldq
pge
pni
popcnt
pse
pse36
rdtscp
rtm
sep
smep
sse
sse2
sse4.1
sse4.2
ssse3
syscall
tsc
tsc-deadline
x2apic
xsave

The following example shows the list of node labels generated by the node-labeller after iterating and comparing the CPU features for Penryn with the CPU features for Haswell:

Example of node labels after iteration

aes
avx
avx2
bmi1
bmi2
erms
fma
fsgsbase
hle
invpcid
movbe
pcid
pclmuldq
popcnt
rdtscp
rtm
sse4.2
tsc-deadline
x2apic
xsave

10.5.2. Configuring a config map for obsolete CPU models

Use this procedure to configure a config map for obsolete CPU models.

Procedure

  • Create a ConfigMap object, specifying the obsolete CPU models in the obsoleteCPUs array. For example: 

    apiVersion: v1
kind: ConfigMap
metadata:
  name: cpu-plugin-configmap 1
data: 2
  cpu-plugin-configmap:
    obsoleteCPUs: 3
      - "486"
      - "pentium"
      - "pentium2"
      - "pentium3"
      - "pentiumpro"
    minCPU: "Penryn" 4
    1
    Name of the config map.
    2
    Configuration data.
    3
    List of obsolete CPU models.
    4
    Minimum CPU model that is used for basic CPU features.