OpenStack建立实例完整过程源码详细分析（5）

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现在开始，开始分析great这个最重要的方法。我们回到第一篇文章中的run_instances方法：

def run_instances(self, context, **kwargs):  
            """ 
            准备实例，并且发送实例的信息和要运行实例的请求消息到远程调度器scheduler； 
            实现实例的简历和运行，由调度器完成； 
            """  

            ......

            # create：准备实例，并且发送实例的信息和要运行实例的请求消息到远程调度器scheduler；  
            # 实现实例的简历和运行，由调度器完成，这部分代码实际上只是实现请求消息的发送；  
            (instances, resv_id) = self.compute_api.create(context,  
                # get_instance_type_by_name：通过给定的name检索单个实例类型信息；  
                # 以字典的形式返回查询结果；  
                instance_type=instance_types.get_instance_type_by_name(kwargs.get('instance_type', None)),  
                image_href=image_uuid,  
                max_count=int(kwargs.get('max_count', min_count)),  
                min_count=min_count,  
                kernel_id=kwargs.get('kernel_id'),  
                ramdisk_id=kwargs.get('ramdisk_id'),  
                key_name=kwargs.get('key_name'),  
                user_data=kwargs.get('user_data'),  
                security_group=kwargs.get('security_group'),  
                availability_zone=kwargs.get('placement', {}).get('availability_zone'),  
                block_device_mapping=kwargs.get('block_device_mapping', {}))  
            return self._format_run_instances(context, resv_id)  

这里调用的是/nova/compute/api.py中的creat方法，这是建立所有类型的实例都要调用的方法；

def create(self, context, instance_type,
               image_href, kernel_id=None, ramdisk_id=None,
               min_count=None, max_count=None,
               display_name=None, display_description=None,
               key_name=None, key_data=None, security_group=None,
               availability_zone=None, user_data=None, metadata=None,
               injected_files=None, admin_password=None,
               block_device_mapping=None, access_ip_v4=None,
               access_ip_v6=None, requested_networks=None, config_drive=None,
               auto_disk_config=None, scheduler_hints=None):
        """
        准备实例，并且发送实例的信息和要运行实例的请求消息到远程调度器scheduler；
        实现实例的简历和运行，由调度器完成，这部分代码实际上只是实现请求消息的发送；
        返回一个元组（实例或者是reservation_id的元组），元组里面的实例可以是“None”或者是实例字典的一个列表，这要取决于是否等待scheduler返回的信息；
        """

        self._check_create_policies(context, availability_zone,requested_networks, block_device_mapping)

        # 验证所有的输入实例参数；
        # 发送要运行实例（'run_instance'）的请求消息到远程调度器；
        return self._create_instance(
                               context, instance_type,
                               image_href, kernel_id, ramdisk_id,
                               min_count, max_count,
                               display_name, display_description,
                               key_name, key_data, security_group,
                               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,
                               scheduler_hints=scheduler_hints)

这里涉及到的参数太多，想看看具体的参数值都是什么，应用命令行：

nova boot --flavor 2 --key_name oskey --image 20612b24-c980-4900-b270-8e6b66e5f72f test3

调试运行了一下，输出的参数值如下：

context = <nova.context.RequestContext object at 0x447d050>
instance_type = {'memory_mb': 2048L, 'root_gb': 20L, 'deleted_at': None, 'name': u'm1.small', 'deleted': 0L, 'created_at': None, 'ephemeral_gb': 0L, 'updated_at': None, 'disabled': False, 'vcpus': 1L, 'extra_specs': {}, 'swap': 0L, 'rxtx_factor': 1.0, 'is_public': True, 'flavorid': u'2', 'vcpu_weight': None, 'id': 5L}
image_href = 20612b24-c980-4900-b270-8e6b66e5f72f
kernel_id = None
ramdisk_id = None
min_count = 1
max_count = 1
display_name = test3
display_description = test3
key_name = oskey
key_data = None
security_group = ['default']
availability_zone = None
user_data = None
metadata = {}
injected_files = []
admin_password = Piu4aSSNmSNk
block_device_mapping = []
access_ip_v4 = None
access_ip_v6 = None
requested_networks = None
config_drive = None
auto_disk_config = None
scheduler_hints = {}

可以看到context这个上下文信息对象，是由类nova.context.RequestContext实例化来的，那我们具体看一下，这个上下文运行环境都包括哪些信息：

class RequestContext(object):

    def __init__(self, user_id, project_id, is_admin=None, read_deleted="no",
                 roles=None, remote_address=None, timestamp=None,
                 request_id=None, auth_token=None, overwrite=True,
                 quota_class=None, user_name=None, project_name=None,
                 service_catalog=None, instance_lock_checked=False, **kwargs):
        
        if kwargs:
            LOG.warn(_('Arguments dropped when creating context: %s') %
                    str(kwargs))

        self.user_id = user_id
        self.project_id = project_id
        self.roles = roles or []
        self.read_deleted = read_deleted
        self.remote_address = remote_address
        if not timestamp:
            timestamp = timeutils.utcnow()
        if isinstance(timestamp, basestring):
            timestamp = timeutils.parse_strtime(timestamp)
        self.timestamp = timestamp
        if not request_id:
            request_id = generate_request_id()
        self.request_id = request_id
        self.auth_token = auth_token

        if service_catalog:
            self.service_catalog = [s for s in service_catalog
                if s.get('type') in ('volume')]
        else:
            self.service_catalog = []

        self.instance_lock_checked = instance_lock_checked

        self.quota_class = quota_class
        self.user_name = user_name
        self.project_name = project_name
        self.is_admin = is_admin
        if self.is_admin is None:
            self.is_admin = policy.check_is_admin(self)
        if overwrite or not hasattr(local.store, 'context'):
            self.update_store()

    ......

我们在看看在这里context中的信息具体值都是什么，会更加有助我们理解context，调试运行一下：

user_id = afc380206e2549ad930396d9050d20cf
project_id = 0e492e86f22e4d19bd523f1e7ca64566
roles = [u'admin', u'KeystoneAdmin', u'KeystoneServiceAdmin']
read_deleted = no
remote_address = 172.21.6.145
timestamp = 2013-06-23 16:36:37.399405
request_id = req-f0255b14-833d-4fff-b973-23c35f70ddda
auth_token = 7e7bb3cf84ab43269010bb55410064b3
service_catalog = [{u'endpoints': [{u'adminURL': u'http://172.21.5.161:8776/v1/0e492e86f22e4d19bd523f1e7ca64566', u'region': u'RegionOne', u'id': u'753a1ad55e91469794e2eb7ac4c3df92', u'internalURL': u'http://172.21.5.161:8776/v1/0e492e86f22e4d19bd523f1e7ca64566', u'publicURL': u'http://172.21.6.145:8776/v1/0e492e86f22e4d19bd523f1e7ca64566'}], u'endpoints_links': [], u'type': u'volume', u'name': u'cinder'}]
instance_lock_checked = False
quota_class = None
user_name = admin
project_name = admin
is_admin = True