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Chapter 10. Live migration

10.1. About live migration
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Live migration is the process of moving a running virtual machine (VM) to another node in the cluster without interrupting the virtual workload. By default, live migration traffic is encrypted using Transport Layer Security (TLS).

10.1.1. Live migration requirements
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Live migration has the following requirements:

  • The cluster must have shared storage with ReadWriteMany (RWX) access mode.

  • The cluster must have sufficient RAM and network bandwidth.

    Note

    You must ensure that there is enough memory request capacity in the cluster to support node drains that result in live migrations. You can determine the approximate required spare memory by using the following calculation: 

    Product of (Maximum number of nodes that can drain in parallel) and (Highest total VM memory request allocations across nodes)
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    The default number of migrations that can run in parallel in the cluster is 5.

  • If a VM uses a host model CPU, the nodes must support the CPU.
  • Configuring a dedicated Multus network for live migration is highly recommended. A dedicated network minimizes the effects of network saturation on tenant workloads during migration.

10.1.2. Common live migration tasks
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You can perform the following live migration tasks:

10.1.3. Additional resources
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10.2. Configuring live migration
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You can configure live migration settings to ensure that the migration processes do not overwhelm the cluster.

You can configure live migration policies to apply different migration configurations to groups of virtual machines (VMs).

10.2.1. Live migration settings
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You can configure the following live migration settings:

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 hyperconverged kubevirt-hyperconverged -n openshift-cnv
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    Example configuration file

    apiVersion: hco.kubevirt.io/v1beta1
kind: HyperConverged
metadata:
  name: kubevirt-hyperconverged
  namespace: openshift-cnv
spec:
  liveMigrationConfig:
    bandwidthPerMigration: 64Mi
    1 
    
    completionTimeoutPerGiB: 800
    2 
    
    parallelMigrationsPerCluster: 5
    3 
    
    parallelOutboundMigrationsPerNode: 2
    4 
    
    progressTimeout: 150
    5
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    1
    Bandwidth limit of each migration, where the value is the quantity of bytes per second. For example, a value of 2048Mi means 2048 MiB/s. Default: 0, which is unlimited.
    2
    The migration is canceled if it has not completed in this time, in seconds per GiB of memory. For example, a VM 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.
    3
    Number of migrations running in parallel in the cluster. Default: 5.
    4
    Maximum number of outbound migrations per node. Default: 2.
    5
    The migration is canceled if memory copy fails to make progress in this time, in seconds. Default: 150.
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. Live migration policies
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You can create live migration policies to apply different migration configurations to groups of VMs that are defined by VM or project labels.

Tip

You can create live migration policies by using the web console.

You can create a live migration policy by using the command line. A live migration policy is applied to selected virtual machines (VMs) by using any combination of labels:

  • VM labels such as size, os, or gpu
  • Project labels such as priority, bandwidth, or hpc-workload

For the policy to apply to a specific group of VMs, all labels on the group of VMs must match the labels of the policy.

Note

If multiple live migration policies apply to a VM, the policy with the greatest number of matching labels takes precedence.

If multiple policies meet this criteria, the policies are sorted by alphabetical order of the matching label keys, and the first one in that order takes precedence.

Procedure

  1. Create a MigrationPolicy object as in the following example: 

    apiVersion: migrations.kubevirt.io/v1alpha1
kind: MigrationPolicy
metadata:
  name: <migration_policy>
spec:
  selectors:
    namespaceSelector:
    1 
    
      hpc-workloads: "True"
      xyz-workloads-type: ""
    virtualMachineInstanceSelector:
    2 
    
      workload-type: "db"
      operating-system: ""
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    1
    Specify project labels.
    2
    Specify VM labels.

  2. Create the migration policy by running the following command: 

    $ oc create -f <migration_policy>.yaml
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10.3. Initiating and canceling live migration
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You can initiate the live migration of a virtual machine (VM) to another node by using the OpenShift Container Platform web console or the command line.

You can cancel a live migration by using the web console or the command line. The VM remains on its original node.

Tip

You can also initiate and cancel live migration by using the virtctl migrate <vm_name> and virtctl migrate-cancel <vm_name> commands.

10.3.1. Initiating live migration
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You can live migrate a running virtual machine (VM) to a different node in the cluster by using the OpenShift Container Platform web console.

Note

The Migrate action is visible to all users but only cluster administrators can initiate a live migration.

Prerequisites

  • The VM must be migratable.
  • If the VM is configured with a host model CPU, the cluster must have an available node that supports the CPU model.

Procedure

  1. Navigate to Virtualization VirtualMachines in the web console.
  2. Select Migrate from the Options menu kebab beside a VM.
  3. Click Migrate.

You can initiate the live migration of a running virtual machine (VM) by using the command line to create a VirtualMachineInstanceMigration object for the VM.

Procedure

  1. Create a VirtualMachineInstanceMigration manifest for the VM that you want to migrate: 

    apiVersion: kubevirt.io/v1
kind: VirtualMachineInstanceMigration
metadata:
  name: <migration_name>
spec:
  vmiName: <vm_name>
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  2. Create the object by running the following command: 

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

Verification

  • Obtain the VM status by running the following command: 

    $ oc describe vmi <vm_name> -n <namespace>
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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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10.3.2. Canceling live migration
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You can cancel the live migration of a virtual machine (VM) by using the OpenShift Container Platform web console.

Procedure

  1. Navigate to Virtualization VirtualMachines in the web console.
  2. Select Cancel Migration on the Options menu kebab beside a VM.

Cancel the live migration of a virtual machine 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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