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Chapter 10. Live migration
10.1. Virtual machine live migration
10.1.1. About live migration
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.
You can use live migration if the following conditions are met:
-
Shared storage with
ReadWriteMany
(RWX) access mode. - Sufficient RAM and network bandwidth.
- If the virtual machine uses a host model CPU, the nodes must support the virtual machine’s host model CPU.
By default, live migration traffic is encrypted using Transport Layer Security (TLS).
10.1.2. Additional resources
10.2. Live migration limits and timeouts
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
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
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
- 1
- In this example, the
spec.liveMigrationConfig
array contains the default values for each field.
NoteYou can restore the default value for any
spec.liveMigrationConfig
field by deleting that key/value pair and saving the file. For example, deleteprogressTimeout: <value>
to restore the defaultprogressTimeout: 150
.
10.2.2. Cluster-wide live migration limits and timeouts
Parameter | Description | Default |
---|---|---|
| Number of migrations running in parallel in the cluster. | 5 |
| Maximum number of outbound migrations per node. | 2 |
| Bandwidth limit of each migration, in MiB/s. | 0 [1] |
|
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 | 800 |
| The migration is canceled if memory copy fails to make progress in this time, in seconds. | 150 |
-
The default value of
0
is unlimited.
10.3. Migrating a virtual machine instance to another node
Manually initiate a live migration of a virtual machine instance to another node using either the web console or the CLI.
If a virtual machine uses a host model CPU, you can perform live migration of that virtual machine only between nodes that support its host CPU model.
10.3.1. Initiating live migration of a virtual machine instance in the web console
Migrate a running virtual machine instance to a different node in the cluster.
The Migrate action is visible to all users but only admin users can initiate a virtual machine migration.
Procedure
-
In the OpenShift Container Platform console, click Virtualization
VirtualMachines from the side menu. You can initiate the migration from this page, which makes it easier to perform actions on multiple virtual machines on the same page, or from the VirtualMachine details page where you can view comprehensive details of the selected virtual machine:
- Click the Options menu next to the virtual machine and select Migrate.
-
Click the virtual machine name to open the VirtualMachine details page and click Actions
Migrate.
- Click Migrate to migrate the virtual machine to another node.
10.3.2. Initiating live migration of a virtual machine instance in the CLI
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
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
Create the object in the cluster by running the following command:
$ oc create -f vmi-migrate.yaml
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. Migrating a virtual machine over a dedicated additional network
You can configure a dedicated Multus network for live migration. A dedicated network minimizes the effects of network saturation on tenant workloads during live migration.
10.4.1. Configuring a dedicated secondary network for virtual machine live migration
To configure a dedicated secondary network for live migration, you must first create a bridge network attachment definition for a namespace by using the CLI. Then, add the name of the NetworkAttachmentDefinition
object to the HyperConverged
custom resource (CR).
Prerequisites
-
You installed the OpenShift CLI (
oc
). -
You logged in to the cluster as a user with the
cluster-admin
role. - The Multus Container Network Interface (CNI) plugin is installed on the cluster.
- Every node on the cluster has at least two Network Interface Cards (NICs), and the NICs to be used for live migration are connected to the same VLAN.
-
The virtual machine (VM) is running with the
LiveMigrate
eviction strategy.
Procedure
Create a
NetworkAttachmentDefinition
manifest.Example configuration file
apiVersion: "k8s.cni.cncf.io/v1" kind: NetworkAttachmentDefinition metadata: name: my-secondary-network 1 namespace: openshift-cnv spec: config: '{ "cniVersion": "0.3.1", "name": "migration-bridge", "type": "macvlan", "master": "eth1", 2 "mode": "bridge", "ipam": { "type": "whereabouts", 3 "range": "10.200.5.0/24" 4 } }'
- 1
- The name of the
NetworkAttachmentDefinition
object. - 2
- The name of the NIC to be used for live migration.
- 3
- The name of the CNI plugin that provides the network for this network attachment definition.
- 4
- The IP address range for the secondary network. This range must not have any overlap with the IP addresses of the main network.
Open the
HyperConverged
CR in your default editor by running the following command:oc edit hyperconverged kubevirt-hyperconverged -n openshift-cnv
Add the name of the
NetworkAttachmentDefinition
object to thespec.liveMigrationConfig
stanza of theHyperConverged
CR. For example:Example configuration file
apiVersion: hco.kubevirt.io/v1beta1 kind: HyperConverged metadata: name: kubevirt-hyperconverged spec: liveMigrationConfig: completionTimeoutPerGiB: 800 network: my-secondary-network 1 parallelMigrationsPerCluster: 5 parallelOutboundMigrationsPerNode: 2 progressTimeout: 150 ...
- 1
- The name of the Multus
NetworkAttachmentDefinition
object to be used for live migrations.
-
Save your changes and exit the editor. The
virt-handler
pods restart and connect to the secondary network.
Verification
When the node that the virtual machine runs on is placed into maintenance mode, the VM automatically migrates to another node in the cluster. You can verify that the migration occurred over the secondary network and not the default pod network by checking the target IP address in the virtual machine instance (VMI) metadata.
oc get vmi <vmi_name> -o jsonpath='{.status.migrationState.targetNodeAddress}'
10.4.2. Additional resources
10.5. Monitoring live migration of a virtual machine instance
You can monitor the progress of a live migration of a virtual machine instance from either the web console or the CLI.
10.5.1. Monitoring live migration of a virtual machine instance in the web console
For the duration of the migration, the virtual machine has a status of Migrating. This status is displayed on the VirtualMachines page or on the VirtualMachine details page of the migrating virtual machine.
Procedure
-
In the OpenShift Container Platform console, click Virtualization
VirtualMachines from the side menu. - Select a virtual machine to open the VirtualMachine details page.
10.5.2. Monitoring live migration of a virtual machine instance in the CLI
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
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
10.6. Cancelling the live migration of a virtual machine instance
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.
10.6.1. Cancelling live migration of a virtual machine instance in the web console
You can cancel the live migration of a virtual machine instance in the web console.
Procedure
-
In the OpenShift Container Platform console, click Virtualization
VirtualMachines from the side menu. - Click the Options menu beside a virtual machine and select Cancel Migration.
10.6.2. Cancelling live migration of a virtual machine instance in the CLI
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
10.7. Configuring virtual machine eviction strategy
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.
10.7.1. Configuring custom virtual machines with the LiveMigration eviction strategy
You only need to configure the LiveMigration
eviction strategy on custom virtual machines. Common templates have this eviction strategy configured by default.
Procedure
Add the
evictionStrategy: LiveMigrate
option to thespec.template.spec
section in the virtual machine configuration file. This example usesoc edit
to update the relevant snippet of theVirtualMachine
configuration file:$ oc edit vm <custom-vm> -n <my-namespace>
apiVersion: kubevirt.io/v1 kind: VirtualMachine metadata: name: custom-vm spec: template: spec: evictionStrategy: LiveMigrate ...
Restart the virtual machine for the update to take effect:
$ virtctl restart <custom-vm> -n <my-namespace>