openstack Neutron分析(3)—— neutron-dhcp-agent源码分析
1.neutron dhcp3个主要部件分别为什么?
2.dhcp模块包含哪些内容?
3.Dnsmasq配置文件是如何创建和更新的?
4.DHCP agent的信息存放在neutron数据库的哪个表中?
扩展: neutron-dhcp-agent在neutron的作用是什么?
一.概述
neutron dhcp为租户网络提供DHCP服务,即IP地址动态分配,另外还会提供metadata请求服务。
3个主要的部件:
DHCP agent scheduler:负责DHCP agent与network的调度
DHCP agent:为租户网络提供DHCP的功能,提供metadata request服务。
DHCP driver:即dnsmasq,用于管理DHCP server。
DHCP agent scheduler:负责DHCP agent与network的调度
DHCP agent:为租户网络提供DHCP的功能,提供metadata request服务。
DHCP driver:即dnsmasq,用于管理DHCP server。
二.REST API
neutron dhcp提供2类REST API接口,这两类API都是extension API。
一种是 Agent Management Extension API:
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![](http://www.aboutyun.com/data/attachment/forum/201410/15/141127n2mkk4dfqq242pp4.png)
另一种是agent调度:
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![](http://www.aboutyun.com/data/attachment/forum/201410/15/141128bci81rbqlqa0847a.png)
三.总体架构
根据整个dhcp处理的流程,dhcp模块主要由Neutron api、core plugin(如linux bridge plugin,ovs plugin等)、dhcp agent scheduler、dhcp agent、dhcp driver(dnsmasq)构成。
架构图如下:
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![](http://www.aboutyun.com/data/attachment/forum/201410/15/141129l3yjjgblfggg433b.jpg)
对应架构图中数字,有以下几个接口:
1.network/subnet/port的操作
2.agent management/agent scheduler的操作
3.network/subnet/port操作会发送rpc请求到dhcp agent。
4.agentscheduler db发送rpc请求到dhcp agent。
5.dhcp agent通过DhcpPluginApi发送rpc请求到core plugin,操作相应的数据库。
6.dhcp agent调用dhcp driver进行dhcp相关操作。
四.代码分析
neutron-dhcp-agent的入口为neutron.agent.dhcp_agent:main,跟l3-agent的启动方式是类似的,都是以Service启动;Manager类为DhcpAgentWithStateReport,汇报DHCPAgent的状态。
- def main():
- register_options()
- common_config.init(sys.argv[1:])
- config.setup_logging(cfg.CONF)
- server = neutron_service.Service.create(
- binary='neutron-dhcp-agent',
- topic=topics.DHCP_AGENT,
- report_interval=cfg.CONF.AGENT.report_interval,
- manager='neutron.agent.dhcp_agent.DhcpAgentWithStateReport')
- service.launch(server).wait()
DhcpAgentWithStateReport继承自DhcpAgent,用于汇报DHCPAgent的状态
- if report_interval:
- self.heartbeat = loopingcall.FixedIntervalLoopingCall(
- self._report_state)
- self.heartbeat.start(interval=report_interval)
_report_state就是从self.cache中取出当前状态,然后构造一个report_state的message发到q-plugin topic的消息队列上。
下面看下DhcpAgent初始化过程:
- def __init__(self, host=None):
- super(DhcpAgent, self).__init__(host=host)
- self.needs_resync_reasons = []
- self.conf = cfg.CONF
- # Agent cache of the current network state
- self.cache = NetworkCache()
- self.root_helper = config.get_root_helper(self.conf)
- # dhcp_driver currently is neutron.agent.linux.dhcp.Dnsmasq
- self.dhcp_driver_cls = importutils.import_class(self.conf.dhcp_driver)
- ctx = context.get_admin_context_without_session()
- # init plugin rpc
- self.plugin_rpc = DhcpPluginApi(topics.PLUGIN, # topic is q-plugin,提供DHCP相关的创建、查询、更新、删除接口
- ctx, self.conf.use_namespaces)
- # create dhcp dir to store dhcp info: /var/lib/neutron/dhcp/
- # these files are used for Dnsmasq
- dhcp_dir = os.path.dirname("/%s/dhcp/" % self.conf.state_path)
- if not os.path.isdir(dhcp_dir):
- os.makedirs(dhcp_dir, 0o755)
- self.dhcp_version = self.dhcp_driver_cls.check_version()
- # query existing_dhcp_networks from driver and then save them into self.cache
- self._populate_networks_cache()
DhcpPluginApi创建了topic为q-plugin的处理方法,dhcp-agent外部可以通过DhcpAgentNotifyAPI来调用这些接口:
- class DhcpAgentNotifyAPI(n_rpc.RpcProxy):
- """API for plugin to notify DHCP agent."""
- BASE_RPC_API_VERSION = '1.0'
- # It seems dhcp agent does not support bulk operation
- VALID_RESOURCES = ['network', 'subnet', 'port']
- VALID_METHOD_NAMES = ['network.create.end',
- 'network.update.end',
- 'network.delete.end',
- 'subnet.create.end',
- 'subnet.update.end',
- 'subnet.delete.end',
- 'port.create.end',
- 'port.update.end',
- 'port.delete.end']
neutron.agent.linux.dhcp.Dnsmasq
DhcpAgent通过self.dhcp_driver_cls = importutils.import_class(self.conf.dhcp_driver)注册了Dnsmasq这个Driver,并在需要的时候调用driver的相应接口:
- def call_driver(self, action, network, **action_kwargs):
- """Invoke an action on a DHCP driver instance."""
- LOG.debug(_('Calling driver for network: %(net)s action: %(action)s'),
- {'net': network.id, 'action': action})
- try:
- # the Driver expects something that is duck typed similar to
- # the base models.
- driver = self.dhcp_driver_cls(self.conf,
- network,
- self.root_helper,
- self.dhcp_version,
- self.plugin_rpc)
- getattr(driver, action)(**action_kwargs)
- return True
Dnsmasq会通过/var/lib/neutron/dhcp/目录下的配置文件启动dnsmasq进程,在DHCP更新的时候,更新这些配置文件并reload配置。
- dnsmasq --no-hosts --no-resolv --strict-order
- --bind-interfaces --interface=tap746570b9-2b --except-interface=lo
- --pid-file=/var/lib/quantum/dhcp/3e16cd2f-c693-49b4-91a7-2a65912ec152/pid
- --dhcp-hostsfile=/var/lib/quantum/dhcp/3e16cd2f-c693-49b4-91a7-2a65912ec152/host
- --dhcp-optsfile=/var/lib/quantum/dhcp/3e16cd2f-c693-49b4-91a7-2a65912ec152/opts
- --dhcp-script=/usr/bin/quantum-dhcp-agent-dnsmasq-lease-update --leasefile-ro
- --dhcp-range=set:tag0,12.0.0.192,static,120s
- --conf-file= --domain=openstacklocal
- --bind-interfaces --interface=tap746570b9-2b
- 主要选项:
- --except-interface=lo 使多个dnsmasq实例可以同时运行在同一台主机上并监听不同的interface
- --dhcp-hostsfile=/var/lib/quantum/dhcp/3e16cd2f-c693-49b4-91a7-2a65912ec152/host 读取IP与虚拟机的静态映射关系,该文件改变后dnsmasq会自动重新加载,不需要重启
- --dhcp-optsfile=/var/lib/quantum/dhcp/3e16cd2f-c693-49b4-91a7-2a65912ec152/opts 指定DNS服务器地址等选项
- --dhcp-script=/usr/bin/quantum-dhcp-agent-dnsmasq-lease-update --leasefile-ro lease信息更新与通知
- --dhcp-range=set:tag0,12.0.0.192,static,120s 重点在于static参数,该参数限制dnsmasq只能为dhcp-hostsfile包含的主机提供DHCP服务
既然Dnsmasq是根据/var/lib/neutron/dhcp/目录下的配置文件启动的,那么这些配置文件是如何创建和更新的呢?
(1)创建过程
dhcp agent在收到network_create_end后,会启动一个dhcp(dnsmasq)进程服务这个新网络。
(2)更新过程
dhcp agent会调用dhcp_driver.reload_allocations来更新配置文件。reload_allocations会根据新网络配置重新生成配置文件。
dhcp agent会在收到如下4种消息时调用reload_allocations
- port_update_end
- port_delete_end
- subnet_update_end
- subnet_delete_end
上面这些通知消息在neturon rest API的前端实现中发出,具体代码在neutron.api.v2.base.py中
- #Controller
- notifier_method = self._resource + '.create.end'
- notifier_method = self._resource + '.delete.end'
- notifier_method = self._resource + '.update.end'
可以看到针对每种resource(network, subnet, port),都会有相应的消息发出。dhcp agent根据这些消息来决定何时重新加载dnsmasp配置文件。
dhcp agent scheduler
通过dhcp agent scheduler,系统中可以部署多个dhcp agent:
1)增加可用性(HA, high availability),避免单点失败(SOF, single point of failure)
2)增加性能,多个dhcp agent可以安装在多台机器上,同时服务。
如何调度dhcp agent
调度算法通过network_scheduler_driver配置,默认是neutron.scheduler.dhcp_agent_scheduler.ChanceScheduler
class ChanceScheduler(object):
"""Allocate a DHCP agent for a network in a random way.
More sophisticated scheduler (similar to filter scheduler in nova?)
can be introduced later.
"""
可以看出,这个实现采用了随机分配算法。
如何调用dhcp agent scheduler
通过neutron.api.rpc.agentnotifiers.dhcp_rpc_agent_api.py中
2)增加性能,多个dhcp agent可以安装在多台机器上,同时服务。
如何调度dhcp agent
调度算法通过network_scheduler_driver配置,默认是neutron.scheduler.dhcp_agent_scheduler.ChanceScheduler
class ChanceScheduler(object):
"""Allocate a DHCP agent for a network in a random way.
More sophisticated scheduler (similar to filter scheduler in nova?)
can be introduced later.
"""
可以看出,这个实现采用了随机分配算法。
如何调用dhcp agent scheduler
通过neutron.api.rpc.agentnotifiers.dhcp_rpc_agent_api.py中
def notify(self, context, data, method_name): 发送消息时,会调用
self._notify_agents,有代码
schedule_required = method == 'port_create_end'
if schedule_required:
agents = self._schedule_network(admin_ctx, network, agents)
可以看到当系统中有新的port创建后,会调用dhcp agent scheduler分配dhcp agent。
self._notify_agents,有代码
schedule_required = method == 'port_create_end'
if schedule_required:
agents = self._schedule_network(admin_ctx, network, agents)
可以看到当系统中有新的port创建后,会调用dhcp agent scheduler分配dhcp agent。
dhcp服务的启动
- def after_start(self):
- self.run()
- LOG.info(_("DHCP agent started"))
- def run(self):
- """Activate the DHCP agent."""
- # 根据系统中的网络配置,启动dhcp服务器进程(dnsmasq)。
- # sync_state()在dhcp agent启动后运行一次。
- self.sync_state()
- # 周期性调用sync_state()
- # dhcp agent会缓存一些网路的信息,通过该任务和neutron同步网络信息,更新本地缓存。
- self.periodic_resync()
neutron的各种插件实现(core plugin or service plugin)都继承于db包下的对象,这些object实现了对相应资源数据模型的操作。
五.类图
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![](http://www.aboutyun.com/data/attachment/forum/201410/15/141133mptpvye8yunvhjt8.jpg)
六.数据库
DHCP agent的信息会存放在neutron数据库的agents表中:
DHCP agent的信息会存放在neutron数据库的agents表中:
- mysql> desc agents;
- +---------------------+---------------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +---------------------+---------------+------+-----+---------+-------+
- | id | varchar(36) | NO | PRI | NULL | |
- | agent_type | varchar(255) | NO | | NULL | |
- | binary | varchar(255) | NO | | NULL | |
- | topic | varchar(255) | NO | | NULL | |
- | host | varchar(255) | NO | | NULL | |
- | admin_state_up | tinyint(1) | NO | | NULL | |
- | created_at | datetime | NO | | NULL | |
- | started_at | datetime | NO | | NULL | |
- | heartbeat_timestamp | datetime | NO | | NULL | |
- | description | varchar(255) | YES | | NULL | |
- | configurations | varchar(4095) | NO | | NULL | |
- +---------------------+---------------+------+-----+---------+-------+
DHCP agent和network绑定关系存储在networkdhcpagentbindings中:
- mysql> desc networkdhcpagentbindings;
- +---------------+-------------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +---------------+-------------+------+-----+---------+-------+
- | network_id | varchar(36) | NO | PRI | NULL | |
- | dhcp_agent_id | varchar(36) | NO | PRI | NULL | |
- +---------------+-------------+------+-----+---------+-------+
agents和networkdhcpagentbindings通过dhcp agent id建立引用关系。
网络,子网和端口信息分别存储在数据库的networks,subnets和ports表中。dhcp agent需要获取这些信息生成dnsmasq的配置信息,并将这些信息存储在/var/lib/neutron/dhcp/目录下。 当neutron-server有需要添加/修改/删除dhcp相关配置时,会将消息发送到队列dhcp_agent.hostname或dhcp_agent_fanout_id,dhcp agent收到消息后进行相应dhcp的配置。
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