Openstack创建虚拟机 Restful api和RPC调用

Horizon前台界面用于接受用户的输入或动作（action），然后将这些参数构造成RESTful API（https://developer.openstack.org/api-ref/compute/#create-server），并通过novaclient发出。Nova-API负责接受该RESTFul API请求，通过RPC调用将消息发送到RabbitMQ，Nova-Compute订阅了该消息，接受消息后随机调用Libvirt API，指挥KVM-QEMU去真正创建虚拟机。

对虚拟机的增删改查（前台）操作，发出的url请求都会被以下模块正则匹配到：

urlpatterns = patterns(
    VIEW_MOD,
    url(r'^$', views.IndexView.as_view(), name='index'),
    url(r'^filter/(?P<vm_state>[^/]+)/$', views.IndexView.as_view(), name='filter'),
    url(r'^create$', views.CreateInstanceView.as_view(), name='create')，
    url(INSTANCES % 'update', views.UpdateView.as_view(), name='update'),
    url(INSTANCES % 'rebuild', views.RebuildView.as_view(), name='rebuild'),

拿创建虚拟机的操作为例，有一系列的步骤（workflow）需要用户选择和操作，目的是拼接足够多的（创建虚拟机所必须的）参数：

class CreateInstanceView(workflows.WorkflowView):
    workflow_class = project_workflows.CreateInstance
    ajax_template_name = constants.INSTANCE_CREATE_TEMPLATE
    success_url = reverse_lazy(constants.INSTANCES_INDEX_URL)

默认的workflow为：

class CreateInstance(workflows.Workflow):
    slug = "create_instance"
    name = _("Create Instance")
    finalize_button_name = _("Create")
    success_message = _('Launched %(count)s named "%(name)s".')
    failure_message = _('Unable to launch %(count)s named "%(name)s".')
    success_url = constants.INSTANCES_INDEX_URL
    wizard = True
    default_steps = (
        SelectImages,
        CustomFlavors,
        SelectHost,
        SelectNetworks,
        SetInstanceDetails
    )

@sensitive_variables('context')
def handle(self, request, context):
    custom_script = context.get('script_data', '')
    vcpus = int(context.get('vcpus', 0))
    ram = int(context.get('ram', 0)) * 1024
    disk = int(float(context.get('disk', 0)))
    count = int(context.get('count', 0))
    pool = context.get('pool', None)
    try:
        rets = api.nova.server_create(request,
                                      context['name'],
                                      image_id,
                                      flavor_id,
                                      None,
                                      normalize_newlines(custom_script),
                                      context['groups']，
                                      meta=meta,
                                      fips=fips)

workflow走完之后，就执行handle方法了，Horizon中有一个api python包，里面有nova,keystone,glance等的api,这些api都是对novaclient、keystoneclient、glanceclient等的封装。

@write_log("Create Server")
def server_create(request, name, image, flavor, key_name, user_data,
                  security_groups, block_device_mapping=None,
                  block_device_mapping_v2=None, nics=None,
                  availability_zone=None, instance_count=1, admin_pass=None,
                  disk_config=None, config_drive=None, meta=None,
                  host=None, fips=None):

    return Server(novaclient(request).servers.create(
        name, image, flavor, userdata=user_data,
        security_groups=security_groups,
        key_name=key_name, block_device_mapping=block_device_mapping,
        block_device_mapping_v2=block_device_mapping_v2,
        nics=nics, availability_zone=availability_zone,
        min_count=instance_count, admin_pass=admin_pass,
        disk_config=disk_config, config_drive=config_drive,
        meta=meta, fips=fips), request)

novaclient的create方法获得需要的参数后，构造Restful api，并发送到Nova服务中，由nova-api负责接收。

在Nova组件中，nova/api/openstack/compute/servers.py（nova-api）的Controller负责接受请求并进行处理。

class Controller(wsgi.Controller):
    def create(self, req, body):
        try:
            _get_inst_type = flavors.get_flavor_by_flavor_id
            inst_type = _get_inst_type(flavor_id, ctxt=context,
                                       read_deleted="no")

            (instances, resv_id) = self.compute_api.create(context,
                        inst_type,
                        image_uuid,
                        display_name=name,
                        display_description=name,
                        key_name=key_name,
                        metadata=server_dict.get('metadata', {}),
                        config_drive=config_drive,
                        block_device_mapping=block_device_mapping,
                        auto_disk_config=auto_disk_config,
                        scheduler_hints=scheduler_hints,
                        legacy_bdm=legacy_bdm,
                        check_server_group_quota=check_server_group_quota,
                        floating_ips=floating_ips)

        return self._add_location(robj)

    def _delete(self, context, req, instance_uuid):
        instance = self._get_server(context, req, instance_uuid)
        if CONF.reclaim_instance_interval:
            try:
                self.compute_api.soft_delete(context, instance)
            except exception.InstanceInvalidState:
                self.compute_api.delete(context, instance)
        else:
            self.compute_api.delete(context, instance)

之后，会调用Nova Compute的api模块的相应方法：

def _create_instance(self, context, instance_type,
           image_href, kernel_id, ramdisk_id,
           min_count, max_count,
           display_name, display_description,
           key_name, key_data, security_groups,
           availability_zone, user_data, metadata,
           injected_files, admin_password,
           access_ip_v4, access_ip_v6,
           requested_networks, config_drive,
           block_device_mapping, auto_disk_config,
           reservation_id=None, scheduler_hints=None,
           legacy_bdm=True, shutdown_terminate=False,
           check_server_group_quota=False,
           floating_ips=None):
    
    self.compute_task_api.build_instances(context,
            instances=instances, image=boot_meta,
            filter_properties=filter_properties,
            admin_password=admin_password,
            injected_files=injected_files,
            requested_networks=requested_networks,
            security_groups=security_groups,
            block_device_mapping=block_device_mapping,
            legacy_bdm=False,
            floating_ips=floating_ips)

    return (instances, reservation_id)

然后，会调用Nova-Conductor API中的ComputeTaskAPI相应方法：

def build_instances(self, context, instances, image, filter_properties,
        admin_password, injected_files, requested_networks,
        security_groups, block_device_mapping, legacy_bdm=True,
        floating_ips=None):
    self.conductor_compute_rpcapi.build_instances(context,
            instances=instances, image=image,
            filter_properties=filter_properties,
            admin_password=admin_password, injected_files=injected_files,
            requested_networks=requested_networks,
            security_groups=security_groups,
            block_device_mapping=block_device_mapping,
            legacy_bdm=legacy_bdm,
            floating_ips=floating_ips)

之后，又会调用Nova-Conductor模块RPCAPI中的相应方法：

def build_instances(self, context, instances, image, filter_properties,
        admin_password, injected_files, requested_networks,
        security_groups, block_device_mapping, legacy_bdm=True, 
        floating_ips=None):
    image_p = jsonutils.to_primitive(image)
    kw = {'instances': instances, 'image': image_p,
           'filter_properties': filter_properties,
           'admin_password': admin_password,
           'injected_files': injected_files,
           'requested_networks': requested_networks,
           'security_groups': security_groups,
           'floating_ips': floating_ips}

    version = '1.9'
    if not self.client.can_send_version('1.9'):
        version = '1.8'
        kw['requested_networks'] = kw['requested_networks'].as_tuples()
    if not self.client.can_send_version('1.7'):
        version = '1.5'
        kw.update({'block_device_mapping': block_device_mapping,
                   'legacy_bdm': legacy_bdm})

    cctxt = self.client.prepare(version=version)
    cctxt.cast(context, 'build_instances', **kw)

该方法会获取messaging模块中的RPCClient，然后通过cast的方式将消息发送到RabbitMQ中。

• RPC.call：发送请求到消息队列，等待返回最终结果。例如nova-compute调用nova-network服务分配网络，需要获得结果。

• RPC.cast：发送请求到消息队列，不需要等待最终返回的结果。例如nova-conductor服务调用nova-compute的build_and_run_instance。

最终，nova-compute订阅了RabbitMQ的消息，接受到创建虚拟机的消息。创建虚拟机的操作，由/nova/compute/manager.py ComputeManager中的_do_build_and_run_instance方法完成。

def _do_build_and_run_instance(self, context, instance, image,
        request_spec, filter_properties, admin_password, injected_files,
        requested_networks, security_groups, block_device_mapping,
        node=None, limits=None,
        floating_ip=None):
    try:
        self._build_and_run_instance(context, instance, image,
                decoded_files, admin_password, requested_networks,
                security_groups, block_device_mapping, node, limits,
                filter_properties,
                floating_ip=floating_ip)

def _build_and_run_instance(self, context, instance, image, injected_files,
        admin_password, requested_networks, security_groups,
        block_device_mapping, node, limits, filter_properties,
        floating_ip=None):
    try:
        self.driver.spawn(context, instance, image,
                          injected_files, admin_password,
                          network_info=network_info,
                          block_device_info=block_device_info)

最后，调用Libvirt（Driver）的api接口，完成创建虚拟机的操作。/nova/virt/libvirt/driver spawn方法为创建本地镜像，获取虚机xml文件，创建domain：

def spawn(self, context, instance, image_meta, injected_files,
          admin_password, network_info=None, block_device_info=None):
    disk_info = blockinfo.get_disk_info(CONF.libvirt.virt_type,
                                        instance,
                                        block_device_info,
                                        image_meta)
    
    self._create_image(context, instance,
                       disk_info['mapping'],
                       network_info=network_info,
                       block_device_info=block_device_info,
                       files=injected_files,
                       admin_pass=admin_password)
    xml = self._get_guest_xml(context, instance, network_info,
                              disk_info, image_meta,
                              block_device_info=block_device_info,
                              write_to_disk=True)
    self._create_domain_and_network(context, xml, instance, network_info,
                                    block_device_info, disk_info=disk_info)
    LOG.debug("Instance is running", instance=instance)