一.Layer-3 Networking Extension
neutron l3作為一種API擴展，向租戶提供了路由和NAT功能。
l3擴展包含兩種資源：
- router：在不同內部子網中轉發數據包；通過指定內部網關做NAT。每一個子網對應router上的一個端口，這個端口的ip就是子網的網關。
- floating ip：代表一個外部網絡的IP，映射到內部網絡的端口上。當網絡的router:external屬性為True時，floating ip才能定義。
這兩種資源都對應有不同的屬性。支持CRUD操作。
二.代碼分析
既然neutron中支持了l3擴展，那么怎樣通過API來創建router或者floating ip，以提供路由以及NAT的功能的呢？
主要有以下幾個步驟：
1.租戶通過horizon，nova命令或者自定義的腳本，發送與router或floating ip相關的操作。
2.這些API請求發送到neutron server，通過neutron提供的API extension相對應。
3.實現這些API extension的操作，比如說create_router，則由具體的plugin和database來共同完成。
4.plugin會通過rpc機制與計算網絡節點上運行的l3 agent來執行l3 轉發和NAT的功能。
l3.py
源代碼目錄：neutron/extensions/l3.py
class RouterPluginBase(object): @abc.abstractmethod def create_router(self, context, router): pass @abc.abstractmethod def update_router(self, context, id, router): pass @abc.abstractmethod def get_router(self, context, id, fields=None): pass @abc.abstractmethod def delete_router(self, context, id): pass @abc.abstractmethod def get_routers(self, context, filters=None, fields=None, sorts=None, limit=None, marker=None, page_reverse=False): pass @abc.abstractmethod def add_router_interface(self, context, router_id, interface_info): pass @abc.abstractmethod def remove_router_interface(self, context, router_id, interface_info): pass @abc.abstractmethod def create_floatingip(self, context, floatingip): pass @abc.abstractmethod def update_floatingip(self, context, id, floatingip): pass @abc.abstractmethod def get_floatingip(self, context, id, fields=None): pass @abc.abstractmethod def delete_floatingip(self, context, id): pass @abc.abstractmethod def get_floatingips(self, context, filters=None, fields=None, sorts=None, limit=None, marker=None, page_reverse=False): pass def get_routers_count(self, context, filters=None): raise NotImplementedError() def get_floatingips_count(self, context, filters=None): raise NotImplementedError()
l3_db.py
源碼目錄：/neutron/db/l3_db.py
這個模塊中，class L3_NAT_db_mixin繼承了上面l3模塊的class RouterPluginBase，因此在RouterPluginBase中定義的抽象方法就要在這里實現了。
類注釋中寫道，Mixin class to add L3/NAT router methods to db_plugin_base_v2。
在類的開始，有這樣一段代碼：
@property def l3_rpc_notifier(self): if not hasattr(self, '_l3_rpc_notifier'): self._l3_rpc_notifier = l3_rpc_agent_api.L3AgentNotifyAPI() return self._l3_rpc_notifier
l3_rpc_agent_api模塊源碼在/neutron/api/rpc/agentnotifiers/l3_rpc_agent_api.py。
class L3AgentNotifyAPI(n_rpc.RpcProxy): """API for plugin to notify L3 agent.""" BASE_RPC_API_VERSION = '1.0' def __init__(self, topic=topics.L3_AGENT): super(L3AgentNotifyAPI, self).__init__( topic=topic, default_version=self.BASE_RPC_API_VERSION) def _notification_host(self, context, method, payload, host): """Notify the agent that is hosting the router.""" ... def _agent_notification(self, context, method, router_ids, operation, data): """Notify changed routers to hosting l3 agents."""
...
def _notification(self, context, method, router_ids, operation, data): """Notify all the agents that are hosting the routers.""" ...def _notification_fanout(self, context, method, router_id): """Fanout the deleted router to all L3 agents.""" ...def agent_updated(self, context, admin_state_up, host): self._notification_host(context, 'agent_updated', {'admin_state_up': admin_state_up}, host) def router_deleted(self, context, router_id): self._notification_fanout(context, 'router_deleted', router_id) def routers_updated(self, context, router_ids, operation=None, data=None): if router_ids: self._notification(context, 'routers_updated', router_ids, operation, data) def router_removed_from_agent(self, context, router_id, host): self._notification_host(context, 'router_removed_from_agent', {'router_id': router_id}, host) def router_added_to_agent(self, context, router_ids, host): self._notification_host(context, 'router_added_to_agent', router_ids, host)
這個類主要用於plugin發送rpc通知給l3 agent。
rpc處理
在上面的l3_db.py中，會將涉及router和floating ip的處理讀取或者寫入到數據中。但是還有一些操作不僅如此，還需要通過rpc（通過調用l3_rpc_agent_api中的函數，這些操作大部分會去 調用routers_updated），通知l3 agent進行處理。
這些需要處理的地方包括：update_router，delete_router，add_router_interface，remove_router_interface，create_floatingip，update_floatingip，delete_floatingip，disassociate_floatingips 等操作。
l3_agent.py
源碼目錄：neutron/agent/l3_agent.py
l3 agent使用Linux ip協議棧和iptables來實現router和NAT的功能。
這時候，如果在horizon的界面創建一個路由，不進行任何操作的話，plugin只會操作數據庫，l3 agent不會作處理。而當update router，如設置外部網關時，l3才會去處理請求。
l3 agent使用service框架啟動服務，其manager類為neutron.agent.l3_agent.L3NATAgentWithStateReport，該類繼承自L3NATAgent，主要實現了基於rpc的_report_state向PluginReportStateAPI(topic為q-plugin)匯報狀態信息，這些信息由各個plugin來處理（比如ml2中通過start_rpc_listeners來注冊該topic的消費者）。
L3NATAgent類是最主要的L3 Manager類，該類繼承關系為 class L3NATAgent(firewall_l3_agent.FWaaSL3AgentRpcCallback, manager.Manager) ；FWaaSL3AgentRpcCallback主要是加載防火牆驅動，並創建RPC與Plugin通信。
再來看L3NATAgent的創建過程：
def __init__(self, host, conf=None): if conf: self.conf = conf else: self.conf = cfg.CONF self.root_helper = config.get_root_helper(self.conf) self.router_info = {} self._check_config_params() try:
# import driver from l3_agent.init
# Example: interface_driver = neutron.agent.linux.interface.OVSInterfaceDriver self.driver = importutils.import_object( self.conf.interface_driver, self.conf ) except Exception: msg = _("Error importing interface driver " "'%s'") % self.conf.interface_driver LOG.error(msg) raise SystemExit(1) self.context = context.get_admin_context_without_session()
＃ Agent side of the l3 agent RPC API, topic is 'q-l3-plugin' self.plugin_rpc = L3PluginApi(topics.L3PLUGIN, host) self.fullsync = True self.updated_routers = set() self.removed_routers = set() self.sync_progress = False self._clean_stale_namespaces = self.conf.use_namespaces # Start RPC Loop self.rpc_loop = loopingcall.FixedIntervalLoopingCall( self._rpc_loop) self.rpc_loop.start(interval=RPC_LOOP_INTERVAL) super(L3NATAgent, self).__init__(conf=self.conf) self.target_ex_net_id = None
上面的self.plugin_rpc會處理neutron-server轉發過來的請求，這個請求是通過service_plugins的方式處理的：
neutron.service_plugins = dummy = neutron.tests.unit.dummy_plugin:DummyServicePlugin router = neutron.services.l3_router.l3_router_plugin:L3RouterPlugin firewall = neutron.services.firewall.fwaas_plugin:FirewallPlugin lbaas = neutron.services.loadbalancer.plugin:LoadBalancerPlugin vpnaas = neutron.services.vpn.plugin:VPNDriverPlugin metering = neutron.services.metering.metering_plugin:MeteringPlugin
self.rpc_loop會循環檢測從plugin發送過來的rpc請求：
@lockutils.synchronized('l3-agent', 'neutron-') def _rpc_loop(self): # _rpc_loop and _sync_routers_task will not be # executed in the same time because of lock. # so we can clear the value of updated_routers # and removed_routers, but they can be updated by # updated_routers and removed_routers rpc call try: LOG.debug(_("Starting RPC loop for %d updated routers"), len(self.updated_routers)) if self.updated_routers: # 保存了需要本次處理的router信息 # We're capturing and clearing the list, and will # process the "captured" updates in this loop, # and any updates that happen due to a context switch # will be picked up on the next pass. updated_routers = set(self.updated_routers) self.updated_routers.clear() router_ids = list(updated_routers) routers = self.plugin_rpc.get_routers( self.context, router_ids) # routers with admin_state_up=false will not be in the fetched fetched = set([r['id'] for r in routers])
＃不在fetched中而在updated_routers中，說明需刪除 self.removed_routers.update(updated_routers - fetched) self._process_routers(routers) self._process_router_delete() LOG.debug(_("RPC loop successfully completed")) except Exception: LOG.exception(_("Failed synchronizing routers")) self.fullsync = True
_process_routers
如果有rpc請求過來，即需要更新路由信息，或者添加路由子接口，創建floating ip等操作，都會在這里執行。這個函數里會去調用_process_routers函數，在_process_routers函數中會去創建綠色線程，執行process_router函數。可以說，l3 agent調用網絡設備的工作都會在process_router中進行。
def process_router(self, ri): ri.iptables_manager.defer_apply_on() ex_gw_port = self._get_ex_gw_port(ri) internal_ports = ri.router.get(l3_constants.INTERFACE_KEY, []) existing_port_ids = set([p['id'] for p in ri.internal_ports]) current_port_ids = set([p['id'] for p in internal_ports if p['admin_state_up']]) new_ports = [p for p in internal_ports if p['id'] in current_port_ids and p['id'] not in existing_port_ids] old_ports = [p for p in ri.internal_ports if p['id'] not in current_port_ids] for p in new_ports: self._set_subnet_info(p) self.internal_network_added(ri, p['network_id'], p['id'], p['ip_cidr'], p['mac_address']) ri.internal_ports.append(p) for p in old_ports: self.internal_network_removed(ri, p['id'], p['ip_cidr']) ri.internal_ports.remove(p) existing_devices = self._get_existing_devices(ri) current_internal_devs = set([n for n in existing_devices if n.startswith(INTERNAL_DEV_PREFIX)]) current_port_devs = set([self.get_internal_device_name(id) for id in current_port_ids]) stale_devs = current_internal_devs - current_port_devs for stale_dev in stale_devs: LOG.debug(_('Deleting stale internal router device: %s'), stale_dev) self.driver.unplug(stale_dev, namespace=ri.ns_name, prefix=INTERNAL_DEV_PREFIX) # Get IPv4 only internal CIDRs internal_cidrs = [p['ip_cidr'] for p in ri.internal_ports if netaddr.IPNetwork(p['ip_cidr']).version == 4] # TODO(salv-orlando): RouterInfo would be a better place for # this logic too ex_gw_port_id = (ex_gw_port and ex_gw_port['id'] or ri.ex_gw_port and ri.ex_gw_port['id']) interface_name = None if ex_gw_port_id: interface_name = self.get_external_device_name(ex_gw_port_id) if ex_gw_port and ex_gw_port != ri.ex_gw_port: self._set_subnet_info(ex_gw_port) self.external_gateway_added(ri, ex_gw_port, interface_name, internal_cidrs) elif not ex_gw_port and ri.ex_gw_port: self.external_gateway_removed(ri, ri.ex_gw_port, interface_name, internal_cidrs) stale_devs = [dev for dev in existing_devices if dev.startswith(EXTERNAL_DEV_PREFIX) and dev != interface_name] for stale_dev in stale_devs: LOG.debug(_('Deleting stale external router device: %s'), stale_dev) self.driver.unplug(stale_dev, bridge=self.conf.external_network_bridge, namespace=ri.ns_name, prefix=EXTERNAL_DEV_PREFIX) # Process static routes for router self.routes_updated(ri) # Process SNAT rules for external gateway ri.perform_snat_action(self._handle_router_snat_rules, internal_cidrs, interface_name) # Process SNAT/DNAT rules for floating IPs fip_statuses = {} try: if ex_gw_port: existing_floating_ips = ri.floating_ips self.process_router_floating_ip_nat_rules(ri) ri.iptables_manager.defer_apply_off() # Once NAT rules for floating IPs are safely in place # configure their addresses on the external gateway port fip_statuses = self.process_router_floating_ip_addresses( ri, ex_gw_port) except Exception: # TODO(salv-orlando): Less broad catching # All floating IPs must be put in error state for fip in ri.router.get(l3_constants.FLOATINGIP_KEY, []): fip_statuses[fip['id']] = l3_constants.FLOATINGIP_STATUS_ERROR if ex_gw_port: # Identify floating IPs which were disabled ri.floating_ips = set(fip_statuses.keys()) for fip_id in existing_floating_ips - ri.floating_ips: fip_statuses[fip_id] = l3_constants.FLOATINGIP_STATUS_DOWN # Update floating IP status on the neutron server self.plugin_rpc.update_floatingip_statuses( self.context, ri.router_id, fip_statuses) # Update ex_gw_port and enable_snat on the router info cache ri.ex_gw_port = ex_gw_port ri.enable_snat = ri.router.get('enable_snat')
1.處理內部接口
這個是在router添加和刪除子接口時工作。它會調用internal_network_added和internal_network_removed這個兩個函數。
在internal_network_added和internal_network_removed這個兩個函數會去調用OVSInterfaceDriver的plug和unplug 函數，這兩個函數最終會用ip link 和ip addr的命令去處理接口和ip地址。
2.處理外部網關
router添加和刪除外部網關。調用external_gateway_added和external_gateway_removed函數，同樣也會調用plug和unplug函數，用ip link 和ip addr的命令進行最終處理
3.為外部網關做SNAT
調用_handle_router_snat_rules函數，使用iptables來加鏈和刪除鏈。
在我的測試網絡中，router上有3個接口，外部網關地址為192.168.39.2，內部兩個子網的網關為10.1.0.1，10.2.0.1。iptables規則如下：
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1
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3
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iptables -t nat -A POSTROUTING ! -i qg-fcb1a762-1f ! -o qg-fcb1a762-1f -m conntrack ! --ctstate DNAT -j ACCEPT
iptables -t nat -A snat -s 10.2.0.1
/24
-j SNAT --to-
source
192.168.39.2
iptables -t nat -A snat -s 10.1.0.1
/24
-j SNAT --to-
source
192.168.39.2
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qg-fcb1a762-1f為外部網關接口的索引，使用ip netns exec $namespace ip link list可查看。
4.為floating ip做SNAT/DNAT
和浮動IP相關，如創建，更新，刪除，綁定到一個雲主機的接口，解綁定等。
不同neutron版本這部分的處理不同，這里是基於Icehouse rc1版本的，在havava stable版本，只有一個函數來處理iptables規則和floating ip。
process_router_floating_ip_nat_rules ：當floating ip與雲主機綁定時，會先清除已有的floating_ip規則，再加上要添加的iptables規則,同時重新加載清除的iptables規則。
比如，一個雲主機10.1.0.2上綁定了一個floating ip（192.168.39.5）。那么最終會在iptable不同的鏈中添加iptables規則，float-snat為neutron自定義鏈。
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iptables -t nat -A PREROUTING -d 192.168.39.5 -j DNAT --to 10.1.0.2
iptables -t nat -A OUTPUT -d 192.168.39.5 -j DNAT --to 10.1.0.2
iptables -t nat -A float-snat -s 10.1.0.2 -j SNAT --to 192.168.39.5
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process_router_floating_ip_addresses：
將floating ip和雲主機綁定時，使用ip addr add命令添加ip地址。
解除floating ip和雲主機綁定時，使用ip addr del命令將floating ip刪除。
類圖
本文轉自http://squarey.me/cloud-virtualization/neutron-l3-analyse.html，有部分刪改。