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Chapter 10. Live migration

10.1. Virtual machine live migration
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10.1.1. Understanding live migration
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Live migration is the process of moving a running virtual machine instance (VMI) to another node in the cluster without interrupting the virtual workload or access. If a VMI uses the LiveMigrate eviction strategy, it automatically migrates when the node that the VMI runs on is placed into maintenance mode. You can also manually start live migration by selecting a VMI to migrate.

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

Note

Live migration is supported for virtual machines that are attached to an SR-IOV network interface only if the sriovLiveMigration feature gate is enabled in the HyperConverged Cluster custom resource (CR). When the spec.featureGates.sriovLiveMigration field is set to true, the virt-launcher pod runs with the SYS_RESOURCE capability. This might degrade its security.

10.1.2. Updating access mode for live migration
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For live migration to function properly, you must use the ReadWriteMany (RWX) access mode. Use this procedure to update the access mode, if needed.

Procedure

  • To set the RWX access mode, run the following oc patch command: 

    $ oc patch -n openshift-cnv \
    cm kubevirt-storage-class-defaults \
    -p '{"data":{"'$<STORAGE_CLASS>'.accessMode":"ReadWriteMany"}}'
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10.2. Live migration limits and timeouts
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Apply live migration limits and timeouts so that migration processes do not overwhelm the cluster. Configure these settings by editing the HyperConverged custom resource (CR).

10.2.1. Configuring live migration limits and timeouts
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Configure live migration limits and timeouts for the cluster by updating the HyperConverged custom resource (CR), which is located in the openshift-cnv namespace.

Procedure

  • Edit the HyperConverged CR and add the necessary live migration parameters. 

    $ oc edit hco -n openshift-cnv kubevirt-hyperconverged
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    Example configuration file

    apiVersion: hco.kubevirt.io/v1beta1
kind: HyperConverged
metadata:
  name: kubevirt-hyperconverged
  namespace: openshift-cnv
spec:
  liveMigrationConfig:
    1 
    
    bandwidthPerMigration: 64Mi
    completionTimeoutPerGiB: 800
    parallelMigrationsPerCluster: 5
    parallelOutboundMigrationsPerNode: 2
    progressTimeout: 150
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    1
    In this example, the spec.liveMigrationConfig array contains the default values for each field.
    Note

    You can restore the default value for any spec.liveMigrationConfig field by deleting that key/value pair and saving the file. For example, delete progressTimeout: <value> to restore the default progressTimeout: 150.

10.2.2. Cluster-wide live migration limits and timeouts
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Expand
Table 10.1. Migration parameters
ParameterDescriptionDefault

parallelMigrationsPerCluster

Number of migrations running in parallel in the cluster.

5

parallelOutboundMigrationsPerNode

Maximum number of outbound migrations per node.

2

bandwidthPerMigration

Bandwidth limit of each migration, in MiB/s.

0 [1]

completionTimeoutPerGiB

The migration is canceled if it has not completed in this time, in seconds per GiB of memory. For example, a virtual machine instance with 6GiB memory times out if it has not completed migration in 4800 seconds. If the Migration Method is BlockMigration, the size of the migrating disks is included in the calculation.

800

progressTimeout

The migration is canceled if memory copy fails to make progress in this time, in seconds.

150

  1. The default value of 0 is unlimited.

10.3. Migrating a virtual machine instance to another node
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Manually initiate a live migration of a virtual machine instance to another node using either the web console or the CLI.

Migrate a running virtual machine instance to a different node in the cluster.

Note

The Migrate Virtual Machine action is visible to all users but only admin users can initiate a virtual machine migration.

Procedure

  1. In the OpenShift Virtualization console, click Workloads Virtualization from the side menu.
  2. Click the Virtual Machines tab.

  3. You can initiate the migration from this screen, which makes it easier to perform actions on multiple virtual machines in the one screen, or from the Virtual Machine Overview screen where you can view comprehensive details of the selected virtual machine:

    • Click the Options menu kebab at the end of virtual machine and select Migrate Virtual Machine.
    • Click the virtual machine name to open the Virtual Machine Overview screen and click Actions Migrate Virtual Machine.
  4. Click Migrate to migrate the virtual machine to another node.

Initiate a live migration of a running virtual machine instance by creating a VirtualMachineInstanceMigration object in the cluster and referencing the name of the virtual machine instance.

Procedure

  1. Create a VirtualMachineInstanceMigration configuration file for the virtual machine instance to migrate. For example, vmi-migrate.yaml: 

    apiVersion: kubevirt.io/v1
kind: VirtualMachineInstanceMigration
metadata:
  name: migration-job
spec:
  vmiName: vmi-fedora
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  2. Create the object in the cluster by running the following command: 

    $ oc create -f vmi-migrate.yaml
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The VirtualMachineInstanceMigration object triggers a live migration of the virtual machine instance. This object exists in the cluster for as long as the virtual machine instance is running, unless manually deleted.

10.4. Monitoring live migration of a virtual machine instance
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You can monitor the progress of a live migration of a virtual machine instance from either the web console or the CLI.

For the duration of the migration, the virtual machine has a status of Migrating. This status is displayed in the Virtual Machines tab or in the Virtual Machine Overview screen for the migrating virtual machine.

Procedure

  1. In the OpenShift Virtualization console, click Workloads Virtualization from the side menu.
  2. Click the Virtual Machines tab.
  3. Select a virtual machine to open the Virtual Machine Overview screen.

The status of the virtual machine migration is stored in the Status component of the VirtualMachineInstance configuration.

Procedure

  • Use the oc describe command on the migrating virtual machine instance: 

    $ oc describe vmi vmi-fedora
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    Example output

    ...
Status:
  Conditions:
    Last Probe Time:       <nil>
    Last Transition Time:  <nil>
    Status:                True
    Type:                  LiveMigratable
  Migration Method:  LiveMigration
  Migration State:
    Completed:                    true
    End Timestamp:                2018-12-24T06:19:42Z
    Migration UID:                d78c8962-0743-11e9-a540-fa163e0c69f1
    Source Node:                  node2.example.com
    Start Timestamp:              2018-12-24T06:19:35Z
    Target Node:                  node1.example.com
    Target Node Address:          10.9.0.18:43891
    Target Node Domain Detected:  true
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10.5. Cancelling the live migration of a virtual machine instance
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Cancel the live migration so that the virtual machine instance remains on the original node.

You can cancel a live migration from either the web console or the CLI.

You can cancel a live migration of the virtual machine instance using the Options menu kebab found on each virtual machine in the Virtualization Virtual Machines tab, or from the Actions menu available on all tabs in the Virtual Machine Overview screen.

Procedure

  1. In the OpenShift Virtualization console, click Workloads Virtualization from the side menu.
  2. Click the Virtual Machines tab.

  3. You can cancel the migration from this screen, which makes it easier to perform actions on multiple virtual machines, or from the Virtual Machine Overview screen where you can view comprehensive details of the selected virtual machine:

    • Click the Options menu kebab at the end of virtual machine and select Cancel Virtual Machine Migration.
    • Select a virtual machine name to open the Virtual Machine Overview screen and click Actions Cancel Virtual Machine Migration.
  4. Click Cancel Migration to cancel the virtual machine live migration.

Cancel the live migration of a virtual machine instance by deleting the VirtualMachineInstanceMigration object associated with the migration.

Procedure

  • Delete the VirtualMachineInstanceMigration object that triggered the live migration, migration-job in this example: 

    $ oc delete vmim migration-job
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10.6. Configuring virtual machine eviction strategy
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The LiveMigrate eviction strategy ensures that a virtual machine instance is not interrupted if the node is placed into maintenance or drained. Virtual machines instances with this eviction strategy will be live migrated to another node.

You only need to configure the LiveMigration eviction strategy on custom virtual machines. Common templates have this eviction strategy configured by default.

Procedure

  1. Add the evictionStrategy: LiveMigrate option to the spec.template.spec section in the virtual machine configuration file. This example uses oc edit to update the relevant snippet of the VirtualMachine configuration file: 

    $ oc edit vm <custom-vm> -n <my-namespace>
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    apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  name: custom-vm
spec:
  template:
    spec:
      evictionStrategy: LiveMigrate
...
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  2. Restart the virtual machine for the update to take effect: 

    $ virtctl restart <custom-vm> -n <my-namespace>
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