openstack.nova.manager创建虚拟机流程(run_instance)

上面的代码整理自 nova/compute/manager.py 代码的顺序有改动，只是为了方便查看，完整的代码可以参考：https://github.com/openstack/nova/blob /master/nova/compute/manager.py

虚拟机的创建流程为3步走：

1. 向nova-network申请IP
2. 向nova-volumn申请block_device
3. 向driver申请创建虚拟机

同时伴随整个过程，虚拟机的vm_state始终是building，但是task_state将会变化三次：

1. networking
2. block_device_mapping
3. spawing

最后，虚拟机的vm_state变成active.

def run_instance(self):
    
    building proccess:

        None
        +
        networking
        |  network_api.allocate_for_instance (nova-network)
        +
        block_device_mapping
        |  setup_block_device_mapping (nova-volumn)
        +
        spawing
        |  driver.spawn (nova-compute.driver)
        +
        Active
    """
    instance = self.db.instance_get_by_uuid(context, instance_uuid)
    self._check_instance_not_already_created(context, instance)
    image_meta = self._check_image_size(context, instance)

    # VM_state = building
    # task_state = None
    self._instance_update(context, instance['uuid'],
                        host=self.host, launched_on=self.host,
                        vm_state=vm_states.BUILDING,
                        task_state=None)

    # VM_state = building
    # task_state = networking
    self._instance_update(context, instance['uuid'],
                        vm_state=vm_states.BUILDING,
                        task_state=task_states.NETWORKING)
    network_info = self.network_api.allocate_for_instance(
                        context, instance, vpn=is_vpn,
                        requested_networks=requested_networks)


    # VM_state = building
    # task_statue = block_device_mapping
    self._instance_update(context, instance['uuid'],
                        vm_state=vm_states.BUILDING,
                        task_state=task_states.BLOCK_DEVICE_MAPPING)
    self._setup_block_device_mapping(context, instance)


    # VM_state = building
    # task_statue = spawing
    self._instance_update(context, instance['uuid'],
                        vm_state=vm_states.BUILDING,
                        task_state=task_states.SPAWNING)
    instance['injected_files'] = injected_files
    instance['admin_pass'] = admin_pass
    self.driver.spawn(context, instance, image_meta,
                        self._legacy_nw_info(network_info), block_device_info)

    # VM_state = active
    # task_statue = None
    self._instance_update(context, instance['uuid'],
                        power_state=current_power_state,
                        vm_state=vm_states.ACTIVE,
                        task_state=None,
                        launched_at=utils.utcnow())