这篇文章将会持续更新，分享使用neutron过程中遇到的那些问题。

问题一：

搭建了控制和计算节点2台虚拟机环境，每台机器上都启动了linux bridge agent,但是通过openstack network agent list命令只能看到计算节点的linux bridge agent.

分析:

有了前面neutron源码的分析积累，我们知道linux bridge agent会向neutron-server定时汇报状态，因此查看这部分源码分析:

neutron/plugins/ml2/plugin.py:

首先是查看ml2 plugin安装的report_state rpc的endpoints:

  @log_helpers.log_method_call
    def start_rpc_listeners(self):
        """Start the RPC loop to let the plugin communicate with agents."""
        self._setup_rpc()
        self.topic = topics.PLUGIN
        self.conn = n_rpc.create_connection()
        self.conn.create_consumer(self.topic, self.endpoints, fanout=False)
        self.conn.create_consumer(
            topics.SERVER_RESOURCE_VERSIONS,
            [resources_rpc.ResourcesPushToServerRpcCallback()],
            fanout=True)
        # process state reports despite dedicated rpc workers
        self.conn.create_consumer(topics.REPORTS,
                                  [agents_db.AgentExtRpcCallback()],
                                  fanout=False)
        return self.conn.consume_in_threads()

可以看到是 agents_db.AgentExtRpcCallback(). 可知会调用其 'report_state' 函数：

neutron/db/agents_db.py:

 @db_api.retry_if_session_inactive()
    def report_state(self, context, **kwargs):
        """Report state from agent to server.

        Returns - agent's status: AGENT_NEW, AGENT_REVIVED, AGENT_ALIVE
        """
        time = kwargs['time']
        time = timeutils.parse_strtime(time)
        agent_state = kwargs['agent_state']['agent_state']
        self._check_clock_sync_on_agent_start(agent_state, time)
        if self.START_TIME > time:
            time_agent = datetime.datetime.isoformat(time)
            time_server = datetime.datetime.isoformat(self.START_TIME)
            log_dict = {'agent_time': time_agent, 'server_time': time_server}
            LOG.debug("Stale message received with timestamp: %(agent_time)s. "
                      "Skipping processing because it's older than the "
                      "server start timestamp: %(server_time)s", log_dict)
            return
        if not self.plugin:
            self.plugin = manager.NeutronManager.get_plugin()
        agent_status, agent_state = self.plugin.create_or_update_agent(
            context, agent_state)
        self._update_local_agent_resource_versions(context, agent_state)
        return agent_status

可以看到会调用ml2插件的'create_or_update_agent'函数,这个函数是ml2 plugin混入的'AgentDbMixin'中的函数:

neutron/db/agents_db.py:

 @db_api.retry_if_session_inactive()
    def create_or_update_agent(self, context, agent_state):
        """Registers new agent in the database or updates existing.

        Returns tuple of agent status and state.
        Status is from server point of view: alive, new or revived.
        It could be used by agent to do some sync with the server if needed.
        """
        status = n_const.AGENT_ALIVE
        with context.session.begin(subtransactions=True):
            res_keys = ['agent_type', 'binary', 'host', 'topic']
            res = dict((k, agent_state[k]) for k in res_keys)
            if 'availability_zone' in agent_state:
                res['availability_zone'] = agent_state['availability_zone']
            configurations_dict = agent_state.get('configurations', {})
            res['configurations'] = jsonutils.dumps(configurations_dict)
            resource_versions_dict = agent_state.get('resource_versions')
            if resource_versions_dict:
                res['resource_versions'] = jsonutils.dumps(
                    resource_versions_dict)
            res['load'] = self._get_agent_load(agent_state)
            current_time = timeutils.utcnow()
            try:
                agent_db = self._get_agent_by_type_and_host(
                    context, agent_state['agent_type'], agent_state['host'])
                if not agent_db.is_active:
                    status = n_const.AGENT_REVIVED
                    if 'resource_versions' not in agent_state:
                        # updating agent_state with resource_versions taken
                        # from db so that
                        # _update_local_agent_resource_versions() will call
                        # version_manager and bring it up to date
                        agent_state['resource_versions'] = self._get_dict(
                            agent_db, 'resource_versions', ignore_missing=True)
                res['heartbeat_timestamp'] = current_time
                if agent_state.get('start_flag'):
                    res['started_at'] = current_time
                greenthread.sleep(0)
                self._log_heartbeat(agent_state, agent_db, configurations_dict)
                agent_db.update(res)
                event_type = events.AFTER_UPDATE
            except ext_agent.AgentNotFoundByTypeHost:
                greenthread.sleep(0)
                res['created_at'] = current_time
                res['started_at'] = current_time
                res['heartbeat_timestamp'] = current_time
                res['admin_state_up'] = cfg.CONF.enable_new_agents
                agent_db = Agent(**res)
                greenthread.sleep(0)
                context.session.add(agent_db)
                event_type = events.AFTER_CREATE
                self._log_heartbeat(agent_state, agent_db, configurations_dict)
                status = n_const.AGENT_NEW
            greenthread.sleep(0)

        registry.notify(resources.AGENT, event_type, self, context=context,
                        host=agent_state['host'], plugin=self,
                        agent=agent_state)
        return status, agent_state

注意红色部分，会根据上报状态的agent的类型和主机名查询数据库，如果已经存在则什么也不做，如果没有存在则会抛出异常 'ext_agent.AgentNotFoundByTypeHost', 然后进行数据库插入操作。这里可以知道neutron-server是用agent类型和主机名做为键值的。

问题原因:

这样问题原因就找到了，因为我的控制节点和计算节点主机名相同，因此只能插入一个agent的信息。修改控制节点主机名后，2个linuxbridge agent就都出来了。