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Configuring Migrations(配置迁移)
Migration allows an administrator to move a virtual machine instance from one compute host to another.
迁移允许管理员能够将虚拟机实例从一台计算主机移动到另一台。
This feature is useful when a compute host requires maintenance.
当一台计算主机需要维护时此功能非常有用。
Migration can also be useful to redistribute the load when many VM instances are running on a specific physical machine.
当为运行着多个虚拟机实例的物理机重新分配负载时迁移也是有用的。
There are two types of migration:
有两种类型的迁移
Migration (or non-live migration): In this case the instance will be shut down (and the instance will know that it has been rebooted) for a period of time in order to be moved to another hypervisor.
迁移（或非实时迁移）：在这种情况下，该虚拟机实例将会在一段时间内被关闭，移到另一台机器上后再重启
Live migration (or true live migration): Almost no instance downtime, it is useful when the instances must be kept running during the migration.
实时迁移：几乎没有实例宕机，当实例必须保持在迁移过程中处于运行状态时它是有用的。
There are two types of live migration:
有两种类型的实时迁移
Shared storage based live migration: In this case both hypervisors have access to a shared storage.
基于共享存储的实时迁移：在这种情况下，两个虚拟机管理程序可以访问共享存储。
Block live migration: for this type of migration, no shared storage is required.
块实时迁移：对于这种类型的迁移，无共享存储是必需的。
The following sections describe how to configure your hosts and compute nodes for migrations using the KVM and XenServer hypervisors.
以下描述如何在主机节点和计算节点上配置KVM和XenServer虚拟机管理程序的迁移。
KVM-Libvirt
Prerequisites
先决条件
Hypervisor: KVM with libvirt
Shared storage: NOVA-INST-DIR/instances/ (eg /var/lib/nova/instances) has to be mounted by shared storage. This guide uses NFS but other options, including the OpenStack Gluster Connector are available.
共享存储：必须通过挂载共享存储。本指南使用NFS，但是其他的选择，包括OpenStack的Gluster的连接器可供选择。
Instances: Instance can be migrated with iSCSI based volumes
实例：实例可以与基于iSCSI的卷迁移
Example Nova Installation Environment
Prepare 3 servers at least; for example, HostA, HostB and HostC
准备至少3台主机，例如：HostA, HostB 和 HostC
HostA is the “Cloud Controller”, and should be running: nova-api, nova-scheduler, nova-network, cinder-volume, nova-objectstore.
HostA是控制节点，运行nova-api, nova-scheduler, nova-network, cinder-volume, nova-objectstore服务
HostB and HostC are the “compute nodes”, running nova-compute.
HostB 和 HostC是计算节点，运行nova-compute服务
Ensure that, NOVA-INST-DIR (set with state_path in nova.conf) is same on all hosts.
确保 NOVA-INST-DIR 在各个节点相同
In this example, HostA will be the NFSv4 server which exports NOVA-INST-DIR/instances, and HostB and HostC mount it.
HostA提供共享存储，HostB 和 HostC挂载到HostA的NOVA-INST-DIR/instances目录下
System configuration
系统配置
1.Configure your DNS or /etc/hosts and ensure it is consistent across all hosts. Make sure that the three hosts can perform name resolution with each other. As a test, use the ping command to ping each host from one another.
在/etc/hosts下配置各个节点的IP和主机名称映射关系，保证各个节点都能够互相ping通
$ ping HostA
$ ping HostB
$ ping HostC
2.Ensure that the UID and GID of your nova and libvirt users are identical between each of your servers. This ensures that the permissions on the NFS mount will work correctly.
确保nova和libvirt在各个节点的用户名是相同的，以便确保对NFS挂载权限可以正常工作
3.Follow the instructions at the Ubuntu NFS HowTo to setup an NFS server on HostA, and NFS Clients on HostB and HostC.
按照在ubuntu上安装NFS说明，在HostA上安装NFS server ，在HostB 和 HostC上安装NFS client
Our aim is to export NOVA-INST-DIR/instances from HostA, and have it readable and writable by the nova user on HostB and HostC.
目的是确保nova用户可以在HostB 和 HostC上读写HostA上的NOVA-INST-DIR/instances目录，实现共享存储
4.Using your knowledge from the Ubuntu documentation, configure the NFS server at HostA by adding a line to /etc/exports
在HostA上的 /etc/exports文件添加以下内容
NOVA-INST-DIR/instances HostA/255.255.0.0(rw,sync,fsid=0,no_root_squash)
Change the subnet mask (255.255.0.0) to the appropriate value to include the IP addresses of HostB and HostC. Then restart the NFS server.
重启 NFS server 服务
$ /etc/init.d/nfs-kernel-server restart
$ /etc/init.d/idmapd restart
5.Set the ‘execute/search’ bit on your shared directory
On both compute nodes, make sure to enable the ‘execute/search’ bit to allow qemu to be able to use the images within the directories. On all hosts, execute the following command:
在每个节点上执行以下命令，NOVA-INST-DIR/instances 增加可执行权限
$ chmod o+x NOVA-INST-DIR/instances
6.Configure NFS at HostB and HostC by adding below to /etc/fstab.
修改HostB和HostC上的/etc/fstab文件，添加以下内容
HostA:/ /NOVA-INST-DIR/instances nfs4 defaults 0 0
Then ensure that the exported directory can be mounted.
确保/NOVA-INST-DIR/instances目录可以挂载
$ mount -a -v
Check that “NOVA-INST-DIR/instances/” directory can be seen at HostA
$ ls -ld NOVA-INST-DIR/instances/
drwxr-xr-x 2 nova nova 4096 2012-05-19 14:34 nova-install-dir/instances/
Perform the same check at HostB and HostC – paying special attention to the permissions (nova should be able to write)
$ ls -ld NOVA-INST-DIR/instances/
drwxr-xr-x 2 nova nova 4096 2012-05-07 14:34 nova-install-dir/instances/
$ df -k
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda1 921514972 4180880 870523828 1% /
none 16498340 1228 16497112 1% /dev
none 16502856 0 16502856 0% /dev/shm
none 16502856 368 16502488 1% /var/run
none 16502856 0 16502856 0% /var/lock
none 16502856 0 16502856 0% /lib/init/rw
HostA: 921515008 101921792 772783104 12% /var/lib/nova/instances ( <— this line is important.)
7.Update the libvirt configurations. Modify /etc/libvirt/libvirtd.conf:
修改libvirt配置文件/etc/libvirt/libvirtd.conf
before : #listen_tls = 0
after : listen_tls = 0
before : #listen_tcp = 1
after : listen_tcp = 1
add: auth_tcp = “none”
Modify /etc/init/libvirt-bin.conf
before : exec /usr/sbin/libvirtd -d
after : exec /usr/sbin/libvirtd -d -l
Modify /etc/default/libvirt-bin
before :libvirtd_opts=” -d”
after :libvirtd_opts=” -d -l”
Restart libvirt. After executing the command, ensure that libvirt is successfully restarted.
$ stop libvirt-bin && start libvirt-bin
$ ps -ef | grep libvirt
root 1145 1 0 Nov27 ? 00:00:03 /usr/sbin/libvirtd -d -l
8.Configure your firewall to allow libvirt to communicate between nodes.
配置防火墙，确保libvirt在各个节点之间通讯
Information about ports used with libvirt can be found at the libvirt documentation By default, libvirt listens on TCP port 16509 and an ephemeral TCP range from 49152 to 49261 is used for the KVM communications. As this guide has disabled libvirt auth, you should take good care that these ports are only open to hosts within your installation.
9.You can now configure options for live migration. In most cases, you do not need to configure any options. The following chart is for advanced usage only.
以下是高级用法，在/etc/nova/nova.conf添加 以下参数
live_migration_bandwidth=0
(IntOpt)Maximum bandwidth to be used during migration, in Mbps
live_migration_flag=VIR_MIGRATE_UNDEFINE_SOURCE, VIR_MIGRATE_PEER2PEER
(StrOpt)Migration flags to be set for live migration
live_migration_retry_count=30
(IntOpt)Number of 1 second retries needed in live_migration
live_migration_uri=qemu+tcp://%s/system
(StrOpt)Migration target URI (any included “%s” is replaced with the migration target hostname)
Enabling true live migration
By default, the Compute service does not use libvirt’s live migration functionality. To enable this functionality, add the following line to nova.conf:
默认情况下，计算服务不启用libvirt的
实时迁移功能，要想启用，添加以下内容
live_migration_flag=VIR_MIGRATE_UNDEFINE_SOURCE,VIR_MIGRATE_PEER2PEER,VIR_MIGRATE_LIVE
The Compute service does not use libvirt’s live miration by default because there is a risk that the migration process will never terminate. This can happen if the guest operating system dirties blocks on the disk faster than they can migrated.
默认情况下，计算服务不启用libvirt的实时迁移功能，原因是有可能出现迁移过程永不停止的风险，客户操作系统弄脏磁盘块的速度比迁移速度快时，就会出现该情况
_______________________________________________________________________________________________________________
Using Migration
使用迁移
Before starting migrations, review the Configuring Migrations section.
在开始迁移之前，请查看配置迁移部分。
Migration provides a scheme to migrate running instances from one OpenStack Compute server to another OpenStack Compute server. This feature can be used as described below.
1, look at the running instances, to get the ID of the instance you wish to migrate.
查看正在运行的实例，获取想要迁移的实例Id
# nova list
+————————————–+——+——–+—————–+
| ID | Name | Status |Networks |
+————————————–+——+——–+—————–+
| d1df1b5a-70c4-4fed-98b7-423362f2c47c | vm1 | ACTIVE | private=a.b.c.d |
| d693db9e-a7cf-45ef-a7c9-b3ecb5f22645 | vm2 | ACTIVE | private=e.f.g.h |
+————————————–+——+——–+—————–+
2, look at information associated with that instance – our example is vm1 from above.
根据ID查看虚拟机实例详细信息
# nova show d1df1b5a-70c4-4fed-98b7-423362f2c47c
+————————————-+———————————————————-+
| Property | Value |
+————————————-+———————————————————-+
…
| OS-EXT-SRV-ATTR:host | HostB |
…
| flavor | m1.tiny |
| id | d1df1b5a-70c4-4fed-98b7-423362f2c47c |
| name | vm1 |
| private network | a.b.c.d |
| status | ACTIVE |
…
+————————————-+———————————————————-+
In this example, vm1 is running on HostB.
3, select the server to migrate instances to.
查看每个节点服务列表
# nova-manage service list
HostA nova-scheduler enabled :-) None
HostA nova-network enabled :-) None
HostB nova-compute enabled :-) None
HostC nova-compute enabled :-) None
In this example, HostC can be picked up because nova-compute is running on it.
4, ensure that HostC has enough resource for migration.
查看HostC资源信息，确保满足迁移
# nova-manage service describe_resource HostC
HOST PROJECT cpu mem(mb) hdd
HostC(total) 16 32232 878
HostC(used_now) 13 21284 442
HostC(used_max) 13 21284 442
HostC p1 5 10240 150
HostC p2 5 10240 150
…..
cpu:the number of cpu
mem(mb):total amount of memory (MB)
hdd:total amount of space for NOVA-INST-DIR/instances(GB)
1st line shows total amount of resource physical server has.
2nd line shows current used resource.
3rd line shows maximum used resource.
4th line and under is used resource per project.
5, use the nova live-migration command to migrate the instances.
执行迁移，将ID为d1df1b5a-70c4-4fed-98b7-423362f2c47c的实例迁移到HostC上
# nova live-migration d1df1b5a-70c4-4fed-98b7-423362f2c47c HostC
Migration of d1df1b5a-70c4-4fed-98b7-423362f2c47c initiated.
Make sure instances are migrated successfully with nova list. If instances are still running on HostB, check logfiles (src/dest nova-compute and nova-scheduler) to determine why.
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