neutron

Can multiple l3-agent instances run on one host?

Asked by Lingxian Kong

Hi all:

When I read the code of the latest quantum master brantch, I found that the behavior of "add_network_to_dhcp_agent" and "add_router_to_l3_agent" is not the same. Because I have not the newest installation for now, so I came here to ask for help!

"add_network_to_dhcp_agent": after some verifacation, will directly add a record in the NetworkDhcpAgentBinding table;

"add_router_to_l3_agent": after some verifacation, method 'auto_schedule_routers' is called:
            result = self.auto_schedule_routers(context,
                                                agent_db.host,
                                                router_id)
the parameter 'agent_db.host' means that there are some l3-agent instances on the host(if not, I think this method will not make sense), then the code will pick one that may be different with the agent you want host the router, so strange!

I wander whether it's a bug. Please let me know if I am missing something here.

--Lingxian Kong

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yong sheng gong
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yong sheng gong (gongysh) said : 		#1

To add route on l3 agent is more complicated, the algorithm is done in auto_schedule_routers. agent_db.host is specifying the agent, the router is the target. so it means add the router to the given l3 agent.

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yong sheng gong (gongysh) said : 		#2

regarding 'Can multiple l3-agent instances run on one host?", the answer is yes, but you should define the 'host' to different value in l3_agent.ini, and the namespace must be enalbed.

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Lingxian Kong (kong) said : 		#3

to yongsheng:

Thanks for your reply!

But I'm still confused. The algorithm in auto_schedule_routers may choose another l3-agent using the same 'host', right?code here:
...
query = context.session.query(agents_db.Agent)
            query = query.filter(agents_db.Agent.agent_type ==
                                 constants.AGENT_TYPE_L3,
                                 agents_db.Agent.host == host,
                                 agents_db.Agent.admin_state_up == True)
            try:
                l3_agent = query.one()
...

and if each l3-agent has different 'host' configuration, why not send message to the agent directly, rather than randomly choose one? I think it's contradictory.

--Lingxian Kong

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Best yong sheng gong (gongysh) said : 		#4

one host can have only one l3 agent. the host is defined by host configuration configuration file, not physical one.
what do u mean by send message to the agent directly? we need to schedule.

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Lingxian Kong (kong) said : 		#5

Thanks yong sheng gong, that solved my question.