OpenStack之虚机热迁移的代码详细解析
话说虚机迁移分为冷迁移以及热迁移，所谓热迁移用度娘的话说即是：热迁移（LiveMigration，又叫动态迁移、实时迁移），即虚机保存/恢复(Save/Restore)：将整个虚拟机的运行状态完整保存下来，同时可以快速的恢复到原有硬件平台甚至是不同硬件平台上。恢复以后，虚机仍旧平滑运行，用户不会察觉到任何差异。OpenStack的虚机迁移是基于Libvirt实现的，下面来看看Openstack虚机热迁移的具体代码实现。
首先，由API入口进入到nova/api/openstack/compute/contrib/admin_actions.py
@wsgi.action('os-migrateLive')
def_migrate_live(self,req,id,body):
"""Permitadminsto(live)migrateaservertoanewhost."""
context=req.environ["nova.context"]
authorize(context,'migrateLive')
try:
block_migration=body["os-migrateLive"]["block_migration"]
disk_over_commit=body["os-migrateLive"]["disk_over_commit"]
host=body["os-migrateLive"]["host"]
except(TypeError,KeyError):
msg=_("host,block_migrationanddisk_over_commitmust"
"bespecifiedforlivemigration.")
raiseexc.HTTPBadRequest(explanation=msg)
try:
block_migration=strutils.bool_from_string(block_migration,
strict=True)
disk_over_commit=strutils.bool_from_string(disk_over_commit,
strict=True)
exceptValueErroraserr:
raiseexc.HTTPBadRequest(explanation=str(err))
try:
instance=self.compute_api.get(context,id,want_objects=True)
self.compute_api.live_migrate(context,instance,block_migration,
disk_over_commit,host)
except(exception.ComputeServiceUnavailable,
exception.InvalidHypervisorType,
exception.UnableToMigrateToSelf,
exception.DestinationHypervisorTooOld,
exception.NoValidHost,
exception.InvalidLocalStorage,
exception.InvalidSharedStorage,
exception.MigrationPreCheckError)asex:
raiseexc.HTTPBadRequest(explanation=ex.format_message())
exceptexception.InstanceNotFoundase:
raiseexc.HTTPNotFound(explanation=e.format_message())
exceptexception.InstanceInvalidStateasstate_error:
common.raise_http_conflict_for_instance_invalid_state(state_error,
'os-migrateLive')
exceptException:
ifhostisNone:
msg=_("Livemigrationofinstance%stoanotherhost"
"failed")%id
else:
msg=_("Livemigrationofinstance%(id)stohost%(host)s"
"failed")%{'id':id,'host':host}
LOG.exception(msg)
#Returnmessagesfromscheduler
raiseexc.HTTPBadRequest(explanation=msg)
returnwebob.Response(status_int=202)
这里第一行可以看到是与API文档的第二行照应的：
{
"os-migrateLive":{
"host":"0443e9a1254044d8b99f35eace132080",
"block_migration":false,
"disk_over_commit":false
}
}
好了，源码中其实执行迁移工作的就是第26、27行的一条语句：
self.compute_api.live_migrate(context,instance,block_migration, disk_over_commit,host)
由这句进入到nova/compute/api.py中，源码如下：
@check_instance_cell
@check_instance_state(vm_state=[vm_states.ACTIVE])
deflive_migrate(self,context,instance,block_migration,
disk_over_commit,host_name):
"""Migrateaserverlivelytoanewhost."""
LOG.debug(_("Goingtotrytolivemigrateinstanceto%s"),
host_nameor"anotherhost",instance=instance)
instance.task_state=task_states.MIGRATING
instance.save(expected_task_state=[None])
self.compute_task_api.live_migrate_instance(context,instance,
host_name,block_migration=block_migration,
disk_over_commit=disk_over_commit)
第2行是一个装饰器，用于在进入API方法之前，检测虚拟机和/或任务的状态，如果实例处于错误的状态，将会引发异常；接下来实时迁移虚机到新的主机，并将虚机状态置于“migrating”,然后由12行进入nova/conductor/api.py
deflive_migrate_instance(self,context,instance,host_name,
block_migration,disk_over_commit):
scheduler_hint={'host':host_name}
self._manager.migrate_server(
context,instance,scheduler_hint,True,False,None,
block_migration,disk_over_commit,None)
将主机名存入字典scheduler_hint中，然后调用nova/conductor/manager.py方法migrate_server,
defmigrate_server(self,context,instance,scheduler_hint,live,rebuild, flavor,block_migration,disk_over_commit,reservations=None): ifinstanceandnotisinstance(instance,instance_obj.Instance): #NOTE(danms):Untilv2oftheRPCAPI,weneedtotolerate #old-worldinstanceobjectshere attrs=['metadata','system_metadata','info_cache', 'security_groups'] instance=instance_obj.Instance._from_db_object( context,instance_obj.Instance(),instance, expected_attrs=attrs) ifliveandnotrebuildandnotflavor: self._live_migrate(context,instance,scheduler_hint, block_migration,disk_over_commit) elifnotliveandnotrebuildandflavor: instance_uuid=instance['uuid'] withcompute_utils.EventReporter(context,self.db, 'cold_migrate',instance_uuid): self._cold_migrate(context,instance,flavor, scheduler_hint['filter_properties'], reservations) else: raiseNotImplementedError()
由于在nova/conductor/api.py中传过来的参数是
self._manager.migrate_server( context,instance,scheduler_hint,True,False,None, block_migration,disk_over_commit,None)
因此live是True，rebuild是Flase,flavor是None，执行第12、13行代码：
ifliveandnotrebuildandnotflavor:
self._live_migrate(context,instance,scheduler_hint,
block_migration,disk_over_commit)
_live_migrate代码如下：
def_live_migrate(self,context,instance,scheduler_hint,
block_migration,disk_over_commit):
destination=scheduler_hint.get("host")
try:
live_migrate.execute(context,instance,destination,
block_migration,disk_over_commit)
except(exception.NoValidHost,
exception.ComputeServiceUnavailable,
exception.InvalidHypervisorType,
exception.InvalidCPUInfo,
exception.UnableToMigrateToSelf,
exception.DestinationHypervisorTooOld,
exception.InvalidLocalStorage,
exception.InvalidSharedStorage,
exception.HypervisorUnavailable,
exception.MigrationPreCheckError)asex:
withexcutils.save_and_reraise_exception():
#TODO(johngarbutt)-eventuallyneedinstanceactionshere
request_spec={'instance_properties':{
'uuid':instance['uuid'],},
}
scheduler_utils.set_vm_state_and_notify(context,
'compute_task','migrate_server',
dict(vm_state=instance['vm_state'],
task_state=None,
expected_task_state=task_states.MIGRATING,),
ex,request_spec,self.db)
exceptExceptionasex:
LOG.error(_('Migrationofinstance%(instance_id)stohost'
'%(dest)sunexpectedlyfailed.'),
{'instance_id':instance['uuid'],'dest':destination},
exc_info=True)
raiseexception.MigrationError(reason=ex)
首先，第三行中将主机名赋给destination,然后执行迁移，后面的都是异常的捕捉，执行迁移的代码分为两部分，先看第一部分，在nova/conductor/tasks/live_migrate.py的184行左右：
defexecute(context,instance,destination, block_migration,disk_over_commit): task=LiveMigrationTask(context,instance, destination, block_migration, disk_over_commit) #TODO(johngarbutt)createasuperclassthatcontainsasafe_executecall returntask.execute()
先创建包含安全执行回调的超类，然后返回如下函数也即执行迁移的第二部分代码，在54行左右：
defexecute(self): self._check_instance_is_running() self._check_host_is_up(self.source) ifnotself.destination: self.destination=self._find_destination() else: self._check_requested_destination() #TODO(johngarbutt)needtomovecomplexityoutofcomputemanager returnself.compute_rpcapi.live_migration(self.context, host=self.source, instance=self.instance, dest=self.destination, block_migration=self.block_migration, migrate_data=self.migrate_data) #TODO(johngarbutt)disk_over_commit?
这里有三部分内容：
如果目前主机不存在，则由调度算法选取一个目标主机，并且进行相关的检测，确保能够进行实时迁移操作；
如果目标主机存在，则直接进行相关的检测操作，确保能够进行实时迁移操作；
执行迁移操作。
前两部分不再赘述，直接看第三部分代码，在nova/compute/rpcapi.py中：
deflive_migration(self,ctxt,instance,dest,block_migration,host,
migrate_data=None):
#NOTE(russellb)Havanacompat
version=self._get_compat_version('3.0','2.0')
instance_p=jsonutils.to_primitive(instance)
cctxt=self.client.prepare(server=host,version=version)
cctxt.cast(ctxt,'live_migration',instance=instance_p,
dest=dest,block_migration=block_migration,
migrate_data=migrate_data)
热迁移开始执行：
deflive_migration(self,context,instance,dest, post_method,recover_method,block_migration=False, migrate_data=None): """Spawninglive_migrationoperationfordistributinghigh-load. :paramcontext:securitycontext :paraminstance: nova.db.sqlalchemy.models.Instanceobject instanceobjectthatismigrated. :paramdest:destinationhost :parampost_method: postoperationmethod. expectednova.compute.manager.post_live_migration. :paramrecover_method: recoverymethodwhenanyexceptionoccurs. expectednova.compute.manager.recover_live_migration. :paramblock_migration:iftrue,doblockmigration. :parammigrate_data:implementationspecificparams """ greenthread.spawn(self._live_migration,context,instance,dest, post_method,recover_method,block_migration, migrate_data)
这个方法中建立一个绿色线程来运行方法_live_migration，来执行实时迁移；主要是调用libvirtpython接口方法virDomainMigrateToURI，来实现从当前主机迁移domain对象到给定的目标主机；
spawn：建立一个绿色线程来运行方法“func(*args,**kwargs)”，这里就是来运行方法_live_migration；
_live_migration：执行实时迁移；主要是调用libvirtpython接口方法virDomainMigrateToURI，来实现从当前主机迁移domain对象到给定的目标主机；
接着在绿色线程中调用_live_migration方法：
def_live_migration(self,context,instance,dest,post_method,
recover_method,block_migration=False,
migrate_data=None):
"""Dolivemigration.
:paramcontext:securitycontext
:paraminstance:
nova.db.sqlalchemy.models.Instanceobject
instanceobjectthatismigrated.
:paramdest:destinationhost
:parampost_method:
postoperationmethod.
expectednova.compute.manager.post_live_migration.
:paramrecover_method:
recoverymethodwhenanyexceptionoccurs.
expectednova.compute.manager.recover_live_migration.
:paramblock_migration:iftrue,doblockmigration.
:parammigrate_data:implementationspecificparams
"""
#Dolivemigration.
try:
ifblock_migration:
flaglist=CONF.libvirt.block_migration_flag.split(',')
else:
flaglist=CONF.libvirt.live_migration_flag.split(',')
flagvals=[getattr(libvirt,x.strip())forxinflaglist]
logical_sum=reduce(lambdax,y:x|y,flagvals)
dom=self._lookup_by_name(instance["name"])
dom.migrateToURI(CONF.libvirt.live_migration_uri%dest,
logical_sum,
None,
CONF.libvirt.live_migration_bandwidth)
exceptExceptionase:
withexcutils.save_and_reraise_exception():
LOG.error(_("LiveMigrationfailure:%s"),e,
instance=instance)
recover_method(context,instance,dest,block_migration)
#Waitingforcompletionoflive_migration.
timer=loopingcall.FixedIntervalLoopingCall(f=None)
ifblock_migration:
flaglist=CONF.libvirt.block_migration_flag.split(',')
这个获取块迁移标志列表，block_migration_flag：这个参数定义了为块迁移设置迁移标志。
else:
flaglist=CONF.libvirt.live_migration_flag.split(',')
flagvals=[getattr(libvirt,x.strip())forxinflaglist]
logical_sum=reduce(lambdax,y:x|y,flagvals)
这部分获取实时迁移标志列表，live_migration_flag这个参数定义了实时迁移的迁移标志。
dom=self._lookup_by_name(instance["name"])
根据给定的实例名称检索libvirt域对象。
timer=loopingcall.FixedIntervalLoopingCall(f=None)
获取等待完成实时迁移的时间。
热迁移代码部分至此结束。
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持毛票票。