OpenStack之虛機熱遷移的代碼詳細(xì)解析

更新時間：2016年11月11日 10:33:51 作者：尛魚

本篇文章主要介紹了OpenStack之虛機熱遷移，有需要的朋友可以了解下。

話說虛機遷移分為冷遷移以及熱遷移，所謂熱遷移用度娘的話說即是：熱遷移（Live Migration，又叫動態(tài)遷移、實時遷移），即虛機保存/恢復(fù)(Save/Restore)：將整個虛擬機的運行狀態(tài)完整保存下來，同時可以快速的恢復(fù)到原有硬件平臺甚至是不同硬件平臺上。恢復(fù)以后，虛機仍舊平滑運行，用戶不會察覺到任何差異。OpenStack的虛機遷移是基于Libvirt實現(xiàn)的，下面來看看Openstack虛機熱遷移的具體代碼實現(xiàn)。

首先，由API入口進(jìn)入到nova/api/openstack/compute/contrib/admin_actions.py

@wsgi.action('os-migrateLive')
  def _migrate_live(self, req, id, body):
    """Permit admins to (live) migrate a server to a new host."""
    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_migration and disk_over_commit must "
          "be specified for live migration.")
      raise exc.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)
    except ValueError as err:
      raise exc.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) as ex:
      raise exc.HTTPBadRequest(explanation=ex.format_message())
    except exception.InstanceNotFound as e:
      raise exc.HTTPNotFound(explanation=e.format_message())
    except exception.InstanceInvalidState as state_error:
      common.raise_http_conflict_for_instance_invalid_state(state_error,
          'os-migrateLive')
    except Exception:
      if host is None:
        msg = _("Live migration of instance %s to another host "
            "failed") % id
      else:
        msg = _("Live migration of instance %(id)s to host %(host)s "
            "failed") % {'id': id, 'host': host}
      LOG.exception(msg)
      # Return messages from scheduler
      raise exc.HTTPBadRequest(explanation=msg)

    return webob.Response(status_int=202)

這里第一行可以看到是與API文檔的第二行照應(yīng)的：

 {
  "os-migrateLive": {
    "host": "0443e9a1254044d8b99f35eace132080",
    "block_migration": false,
    "disk_over_commit": false
  }
}

好了，源碼中其實執(zhí)行遷移工作的就是第26、27行的一條語句：

self.compute_api.live_migrate(context, instance, block_migration,
                 disk_over_commit, host)

由這句進(jìn)入到nova/compute/api.py中，源碼如下：

@check_instance_cell
  @check_instance_state(vm_state=[vm_states.ACTIVE])
  def live_migrate(self, context, instance, block_migration,
           disk_over_commit, host_name):
    """Migrate a server lively to a new host."""
    LOG.debug(_("Going to try to live migrate instance to %s"),
         host_name or "another host", 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行是一個裝飾器，用于在進(jìn)入API方法之前，檢測虛擬機和/或任務(wù)的狀態(tài)，如果實例處于錯誤的狀態(tài)，將會引發(fā)異常；接下來實時遷移虛機到新的主機，并將虛機狀態(tài)置于“migrating”,然后由12行進(jìn)入nova/conductor/api.py

def live_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)

將主機名存入字典scheduler_hint中，然后調(diào)用nova/conductor/manager.py方法migrate_server,

def migrate_server(self, context, instance, scheduler_hint, live, rebuild,
      flavor, block_migration, disk_over_commit, reservations=None):
    if instance and not isinstance(instance, instance_obj.Instance):
      # NOTE(danms): Until v2 of the RPC API, we need to tolerate
      # old-world instance objects here
      attrs = ['metadata', 'system_metadata', 'info_cache',
           'security_groups']
      instance = instance_obj.Instance._from_db_object(
        context, instance_obj.Instance(), instance,
        expected_attrs=attrs)
    if live and not rebuild and not flavor:
      self._live_migrate(context, instance, scheduler_hint,
                block_migration, disk_over_commit)
    elif not live and not rebuild and flavor:
      instance_uuid = instance['uuid']
      with compute_utils.EventReporter(context, self.db,
                     'cold_migrate', instance_uuid):
        self._cold_migrate(context, instance, flavor,
                  scheduler_hint['filter_properties'],
                  reservations)
    else:
      raise NotImplementedError()

由于在nova/conductor/api.py中傳過來的參數(shù)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，執(zhí)行第12、13行代碼：

 if live and not rebuild and not flavor:
       self._live_migrate(context, instance, scheduler_hint,
                block_migration, disk_over_commit) 
　_live_migrate代碼如下：
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) as ex:
      with excutils.save_and_reraise_exception():
        #TODO(johngarbutt) - eventually need instance actions here
        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)
    except Exception as ex:
      LOG.error(_('Migration of instance %(instance_id)s to host'
            ' %(dest)s unexpectedly failed.'),
            {'instance_id': instance['uuid'], 'dest': destination},
            exc_info=True)
      raise exception.MigrationError(reason=ex)

首先，第三行中將主機名賦給destination,然后執(zhí)行遷移，后面的都是異常的捕捉，執(zhí)行遷移的代碼分為兩部分，先看第一部分，在nova/conductor/tasks/live_migrate.py的184行左右：

def execute(context, instance, destination,
      block_migration, disk_over_commit):
  task = LiveMigrationTask(context, instance,
               destination,
               block_migration,
               disk_over_commit)
  #TODO(johngarbutt) create a superclass that contains a safe_execute call
  return task.execute()

先創(chuàng)建包含安全執(zhí)行回調(diào)的超類，然后返回如下函數(shù)也即執(zhí)行遷移的第二部分代碼，在54行左右：

def execute(self):
    self._check_instance_is_running()
    self._check_host_is_up(self.source)

    if not self.destination:
      self.destination = self._find_destination()
    else:
      self._check_requested_destination()

    #TODO(johngarbutt) need to move complexity out of compute manager
    return self.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?

這里有三部分內(nèi)容：

如果目前主機不存在，則由調(diào)度算法選取一個目標(biāo)主機，并且進(jìn)行相關(guān)的檢測，確保能夠進(jìn)行實時遷移操作；

如果目標(biāo)主機存在，則直接進(jìn)行相關(guān)的檢測操作，確保能夠進(jìn)行實時遷移操作；

執(zhí)行遷移操作。

前兩部分不再贅述，直接看第三部分代碼，在nova/compute/rpcapi.py中：

def live_migration(self, ctxt, instance, dest, block_migration, host,
            migrate_data=None):
    # NOTE(russellb) Havana compat
    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)

熱遷移開始執(zhí)行：

def live_migration(self, context, instance, dest,
            post_method, recover_method, block_migration=False,
            migrate_data=None):
    """Spawning live_migration operation for distributing high-load.

    :param context: security context
    :param instance:
      nova.db.sqlalchemy.models.Instance object
      instance object that is migrated.
    :param dest: destination host
    :param post_method:
      post operation method.
      expected nova.compute.manager.post_live_migration.
    :param recover_method:
      recovery method when any exception occurs.
      expected nova.compute.manager.recover_live_migration.
    :param block_migration: if true, do block migration.
    :param migrate_data: implementation specific params

    """

    greenthread.spawn(self._live_migration, context, instance, dest,
             post_method, recover_method, block_migration,
             migrate_data)

這個方法中建立一個綠色線程來運行方法_live_migration，來執(zhí)行實時遷移；主要是調(diào)用libvirt python接口方法virDomainMigrateToURI，來實現(xiàn)從當(dāng)前主機遷移domain對象到給定的目標(biāo)主機；

spawn：建立一個綠色線程來運行方法“func(*args, **kwargs)”，這里就是來運行方法_live_migration；

_live_migration：執(zhí)行實時遷移；主要是調(diào)用libvirt python接口方法virDomainMigrateToURI，來實現(xiàn)從當(dāng)前主機遷移domain對象到給定的目標(biāo)主機；

接著在綠色線程中調(diào)用_live_migration方法：

def _live_migration(self, context, instance, dest, post_method,
            recover_method, block_migration=False,
            migrate_data=None):
    """Do live migration.

    :param context: security context
    :param instance:
      nova.db.sqlalchemy.models.Instance object
      instance object that is migrated.
    :param dest: destination host
    :param post_method:
      post operation method.
      expected nova.compute.manager.post_live_migration.
    :param recover_method:
      recovery method when any exception occurs.
      expected nova.compute.manager.recover_live_migration.
    :param block_migration: if true, do block migration.
    :param migrate_data: implementation specific params
    """

    # Do live migration.
    try:
      if block_migration:
        flaglist = CONF.libvirt.block_migration_flag.split(',')
      else:
        flaglist = CONF.libvirt.live_migration_flag.split(',')
      flagvals = [getattr(libvirt, x.strip()) for x in flaglist]
      logical_sum = reduce(lambda x, 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)

    except Exception as e:
      with excutils.save_and_reraise_exception():
        LOG.error(_("Live Migration failure: %s"), e,
             instance=instance)
        recover_method(context, instance, dest, block_migration)

    # Waiting for completion of live_migration.
    timer = loopingcall.FixedIntervalLoopingCall(f=None)

if block_migration:
         flaglist = CONF.libvirt.block_migration_flag.split(',')

這個獲取塊遷移標(biāo)志列表，block_migration_flag：這個參數(shù)定義了為塊遷移設(shè)置遷移標(biāo)志。

else:
         flaglist = CONF.libvirt.live_migration_flag.split(',')
       flagvals = [getattr(libvirt, x.strip()) for x in flaglist]
      logical_sum = reduce(lambda x, y: x | y, flagvals)

這部分獲取實時遷移標(biāo)志列表，live_migration_flag這個參數(shù)定義了實時遷移的遷移標(biāo)志。

 dom = self._lookup_by_name(instance["name"])

根據(jù)給定的實例名稱檢索libvirt域?qū)ο蟆?/p>

 timer = loopingcall.FixedIntervalLoopingCall(f=None)

獲取等待完成實時遷移的時間。

熱遷移代碼部分至此結(jié)束。

以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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