we could disable l3-agent in a networknode in ha model, then create router,then restart the l3-agent ，we will see the root problem。
but in the network node which has been rebooted ,i can find the qrouter namespace of the new router,but i can't see the snat namespace,so appear the followint problem:

2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent   File "/usr/local/lib/python2.7/dist-packages/neutron/agent/l3/agent.py", line 503, in _process_router_update
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent     self._process_router_if_compatible(router)
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent   File "/usr/local/lib/python2.7/dist-packages/neutron/agent/l3/agent.py", line 440, in _process_router_if_compatible
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent     self._process_added_router(router)
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent   File "/usr/local/lib/python2.7/dist-packages/neutron/agent/l3/agent.py", line 350, in _router_added
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent     super(DvrEdgeHaRouter, self).initialize(process_monitor)
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent   File "/usr/local/lib/python2.7/dist-packages/neutron/agent/l3/ha_router.py", line 87, in initialize
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent     self.ha_network_added()
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent   File "/usr/local/lib/python2.7/dist-packages/neutron/agent/l3/ha_router.py", line 148, in ha_network_added
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent     mtu=self.ha_port.get('mtu'))
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent   File "/usr/local/lib/python2.7/dist-packages/neutron/agent/linux/interface.py", line 249, in plug
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent     bridge, namespace, prefix, mtu)
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent   File "/usr/local/lib/python2.7/dist-packages/neutron/agent/linux/interface.py", line 342, in plug_new
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent     namespace_obj = ip.ensure_namespace(namespace)
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent   File "/usr/local/lib/python2.7/dist-packages/neutron/agent/linux/ip_lib.py", line 197, in ensure_namespace
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent     lo.link.set_up()
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent   File "/usr/local/lib/python2.7/dist-packages/neutron/agent/linux/ip_lib.py", line 504, in set_up
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent     return self._as_root([], ('set', self.name, 'up'))
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent   File "/usr/local/lib/python2.7/dist-packages/neutron/agent/linux/ip_lib.py", line 361, in _as_root
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent     use_root_namespace=use_root_namespace)
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent   File "/usr/local/lib/python2.7/dist-packages/neutron/agent/linux/ip_lib.py", line 94, in _as_root
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent     log_fail_as_error=self.log_fail_as_error)
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent   File "/usr/local/lib/python2.7/dist-packages/neutron/agent/linux/ip_lib.py", line 103, in _execute
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent     log_fail_as_error=log_fail_as_error)
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent   File "/usr/local/lib/python2.7/dist-packages/neutron/agent/linux/utils.py", line 140, in execute
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent     raise RuntimeError(msg)
2016-10-18 17:12:14.170 1303 ERROR neutron.agent.l3.agent RuntimeError: Exit code: 1; Stdin: ; Stdout: ; Stderr: Cannot open network namespace "snat-845e5c46-0743-4b3e-94bf-fd294b03bb7d": No such file or directory