这篇文章是基于KVM作为虚拟机管理程序的假设，而Openstack在RHEL6.4之上的Grizzly上运行。
Openstack VM 实时迁移可以有 3 个类别：
阻止没有共享存储的实时迁移
基于共享存储的实时迁移
卷支持的 VM 实时迁移
阻止实时迁移
块实时迁移不需要 nova 计算节点之间的共享存储，它使用 network（TCP） 将 VM 磁盘从源主机复制到目标主机，因此完成的时间比基于共享存储的实时迁移要长。此外，在迁移过程中，从网络和 CPU 的角度来看，主机性能将会降低。
要启用块实时迁移，我们需要更改每个 nova 计算主机上的 libvirtd 和 nova.conf 配置：
->编辑/etc/libvirt/libvirtd.conf
listen_tls = 0
listen_tcp = 1
auth_tcp = “none”
->编辑/etc/sysconfig/libvirtd
LIBVIRTD_ARGS=”–listen”
->重新启动libvirtd
service libvirtd restart
->编辑 ，添加以下行：/etc/nova/nova.conf
live_migration_flag=VIR_MIGRATE_UNDEFINE_SOURCE,VIR_MIGRATE_PEER2PEER,VIR_MIGRATE_LIVE
添加此行是要求 nova-compute 利用 libvirt 的真正实时迁移函数。默认情况下，由 nova-compute 完成的迁移不使用 libvirt 的实时迁移功能，这意味着来宾在迁移之前被挂起，因此可能会经历几分钟的停机时间。
->重新启动 nova-compute service
service openstack-nova-compute restart
->检查正在运行的虚拟机
nova list
+————————————–+——————-+——–+———————+
| ID | Name | Status | Networks |
+————————————–+——————-+——–+———————+
| 5374577e-7417-4add-b23f-06de3b42c410 | vm-live-migration | ACTIVE | ncep-net=10.20.20.3 |
+————————————–+——————-+——–+———————+
->检查 VM 在哪个主机上运行
nova show vm-live-migration
+————————————-+———————————————————-+
| Property | Value |
+————————————-+———————————————————-+
| status | ACTIVE |
| updated | 2013-08-06T08:47:13Z |
| OS-EXT-STS:task_state | None |
| OS-EXT-SRV-ATTR:host | **compute-1** |
->检查所有可用的主机
nova host-list
+————–+————-+———-+
| host_name | service | zone |
+————–+————-+———-+
| **compute-1** | compute | nova |
| **compute-2** | compute | nova |
->让我们将 vm 迁移到托管计算-2
nova live-migration –block-migrate vm-live-migration compute-2
->当我们再次检查 vm 状态时，我们云上看到主机更改为 compute-2
nova show vm-live-migration
+————————————-+———————————————————-+
| Property | Value |
+————————————-+———————————————————-+
| status | ACTIVE |
| updated | 2013-08-06T09:45:33Z |
| OS-EXT-STS:task_state | None |
| OS-EXT-SRV-ATTR:host | **compute-2** |
->We can just do a migration without specifying destination host, nova-scheduler will choose a free host for you
nova live-migration –block-migrate vm-live-migration
Block live migration seems a good solution if we don’t have/want shared storage , but we still want to do some host level maintenance work without bring downtime to running VMs.
Shared storage based live migration
This example we use GlusterFS as shared storage for nova-compute nodes. Since VM disk is stored on shared storage, hence live migration much much more faster than block live migration.
1.Setup GlusterFS cluster for nova-compute nodes
->Prepare 4 nodes, each node has an extra disk other than OS disk, dedicated for GlusterFS cluster
Node 1: 10.68.124.18 /dev/sdb 1TB
Node 2: 10.68.124.19 /dev/sdb 1TB
Node 3: 10.68.124.20 /dev/sdb 1TB
Node 4: 10.68.124.21 /dev/sdb 1TB
->Configure Node 1-4
yum install -y xfsprogs.x86_64
mkfs.xfs -f -i size=512 /dev/sdb
mkdir /brick1
echo “/dev/sdb /brick1 xfs defaults 1 2” >> /etc/fstab 1014 cat /etc/fstab
mount -a && mount
mkdir /brick1/sdb
yum install glusterfs-fuse glusterfs-server
/etc/init.d/glusterd start
chkconfig glusterd on
->On Node-1, add peers
gluster peer probe 10.68.125.19
gluster peer probe 10.68.125.20
gluster peer probe 10.68.125.21
->On node-1, create a volume for nova-compute
gluster volume create nova-gluster-vol replica 2 10.68.125.18:/brick1/sdb \
10.68.125.19:/brick1/sdb 10.68.125.20:/brick1/sdb 10.68.125.21:/brick1/sdb
gluster volume start nova-gluster-vol
->We can check the volume information
gluster volume info
Volume Name: nova-gluster-vol
Type: Distributed-Replicate
Status: Started
Number of Bricks: 2 x 2 = 4
Transport-type: tcp
Bricks:
Brick1: 10.68.125.18:/brick1/sdb
Brick2: 10.68.125.19:/brick1/sdb
Brick3: 10.68.125.20:/brick1/sdb
Brick4: 10.68.125.21:/brick1/sdb
->On each nova-compute node, mount the GluserFS volume to /var/lib/nova/instances
yum install glusterfs-fuse
mount.glusterfs 10.68.125.18:/nova-gluster-vol /var/lib/nova/instances
echo “10.68.125.18:/nova-gluster-vol /var/lib/nova/instances glusterfs defaults 1 2” >> /etc/fstab
chown -R nova:nova /var/lib/nova/instances
->Edit /etc/libvirt/libvirtd.conf
listen_tls = 0
listen_tcp = 1
auth_tcp = “none”
->Edit /etc/sysconfig/libvirtd
LIBVIRTD_ARGS=”–listen”
->Restart libvirtd
service libvirtd restart
->Edit , add following line:/etc/nova/nova.conf
live_migration_flag=VIR_MIGRATE_UNDEFINE_SOURCE,VIR_MIGRATE_PEER2PEER,VIR_MIGRATE_LIVE
3.Let’s try live migration
->Check running VMs
nova list
+————————————–+——————-+——–+———————+
| ID | Name | Status | Networks |
+————————————–+——————-+——–+———————+
| 5374577e-7417-4add-b23f-06de3b42c410 | vm-live-migration | ACTIVE | ncep-net=10.20.20.3 |
+————————————–+——————-+——–+———————+
->Check which host the VM in running on
nova show vm-live-migration
+————————————-+———————————————————-+
| Property | Value |
+————————————-+———————————————————-+
| status | ACTIVE |
| updated | 2013-08-06T08:47:13Z |
| OS-EXT-STS:task_state | None |
| OS-EXT-SRV-ATTR:host | **compute-1** |
->Check all available hosts
nova host-list
+————–+————-+———-+
| host_name | service | zone |
+————–+————-+———-+
| **compute-1** | compute | nova |
| **compute-2** | compute | nova |
->Let’s migrate the vm to host compute-2
nova live-migration vm-live-migration compute-2
->Migration should be finished in seconds, let’s check vm status again, we cloud see the host changes to compute-2
nova show vm-live-migration
+————————————-+———————————————————-+
| Property | Value |
+————————————-+———————————————————-+
| status | ACTIVE |
| updated | 2013-08-06T09:45:33Z |
| OS-EXT-STS:task_state | None |
| OS-EXT-SRV-ATTR:host | **compute-2** |
->We can just do a migration without specifying destination host, nova-scheduler will choose a free host for us
nova live-migration vm-live-migration
3.Volume backed VM live migration
VMs booted from volume can be also easily and quickly migrated just like shared storage based live migration since both cases VM disks are on top of shared storages.
->Create a bootable volume from an existing image
cinder create –image-id <id of registered image in glance> –display-name bootable-vol-rhel6.3 5
->Launch a VM from the bootable volume
nova boot –image <id of any image in glance, not used but needed> –flavor m1.medium –block_device_mapping vda=<id of bootable vol created above>:::0 vm-boot-from-vol
->Check which host the VM is running on
nova show vm-boot-from-vol
+————————————-+———————————————————-+
| Property | Value |
+————————————-+———————————————————-+
| status | ACTIVE |
| updated | 2013-08-06T10:29:09Z |
| OS-EXT-STS:task_state | None |
| OS-EXT-SRV-ATTR:host | **compute-1** |
->Do live migration
nova live-migration vm-boot-from-vol
->Check VM status again
nova show vm-boot-from-vol
+————————————-+———————————————————-+
| Property | Value |
+————————————-+———————————————————-+
| status | ACTIVE |
| updated | 2013-08-06T10:30:55Z |
| OS-EXT-STS:task_state | None |
| OS-EXT-SRV-ATTR:host | **compute-2** |
VM recovery from failed compute node
If shared storage used, or for VMs booted from volume, we can recovery them if their compute host is failed.
->Launch 1 normal VM and 1 volume backed VM, make they are all running on compute1 node. ( Use live migration if they are not on compute-1)
nova show vm-live-migration
+————————————-+———————————————————-+
| Property | Value |
+————————————-+———————————————————-+
| status | ACTIVE |
| updated | 2013-08-06T10:36:35Z |
| OS-EXT-STS:task_state | None |
| OS-EXT-SRV-ATTR:host | **compute-1** |
nova show vm-boot-from-vol
+————————————-+———————————————————-+
| Property | Value |
+————————————-+———————————————————-+
| status | ACTIVE |
| updated | 2013-08-06T10:31:21Z |
| OS-EXT-STS:task_state | None |
| OS-EXT-SRV-ATTR:host | **compute-1** |
->Shutdown compute-1 node
shutdown now
->Check VM status
nova list
+————————————–+——————-+———+———————+
| ID | Name | Status | Networks |
+————————————–+——————-+———+———————+
| 75ddb4f6-9831-4d90-b291-48e098e8f72f | vm-boot-from-vol | SHUTOFF | ncep-net=10.20.20.5 |
| 5374577e-7417-4add-b23f-06de3b42c410 | vm-live-migration | SHUTOFF | ncep-net=10.20.20.3 |
+————————————–+——————-+———+———————+
Both VMs get into “SHUTOFF” status.
->Recovery them to compute-2 node
nova evacuate vm-boot-from-vol compute-2 –on-shared-storage
nova evacuate vm-live-migration compute-2 –on-shared-storage
->Check VM status
nova show vm-boot-from-vol
+————————————-+———————————————————-+
| Property | Value |
+————————————-+———————————————————-+
| status | SHUTOFF |
| updated | 2013-08-06T10:42:32Z |
| OS-EXT-STS:task_state | None |
| OS-EXT-SRV-ATTR:host | **compute-2** |
nova show vm-live-migration
+————————————-+———————————————————-+
| Property | Value |
+————————————-+———————————————————-+
| status | SHUTOFF |
| updated | 2013-08-06T10:42:51Z |
| OS-EXT-STS:task_state | None |
| OS-EXT-SRV-ATTR:host | **compute-2** |
两个 VM 现在都由 compute-2 管理
->重新启动 2 个虚拟机
nova reboot vm-boot-from-vol
nova reboot vm-live-migration
-> 检查虚拟机列表
nova list
+————————————–+——————-+——–+———————+
| ID | Name | Status | Networks |
+————————————–+——————-+——–+———————+
| 75ddb4f6-9831-4d90-b291-48e098e8f72f | vm-boot-from-vol | ACTIVE | ncep-net=10.20.20.5 |
| 5374577e-7417-4add-b23f-06de3b42c410 | vm-live-migration | ACTIVE | ncep-net=10.20.20.3 |
+————————————–+——————-+——–+———————+
两个 VM 都已恢复为活动状态。
笔记
目前，Openstack没有机制来检测主机和虚拟机故障并自动恢复/迁移虚拟机到健康主机，这种对第三方的回复意味着这样做
还有一个名为openstack-neat的有趣项目，旨在提供OpenStack的扩展，使用实时迁移实现虚拟机（VM）的动态整合。动态虚拟机整合的主要目标是，根据实时资源需求，使用实时迁移重新分配虚拟机，并将空闲主机切换到休眠模式，从而提高物理资源的利用率并降低能耗。这真的像vSphere DRS功能。
项目网站：http://openstack-neat.org
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