Re: ipvs connection synchronization

 ❦  4 février 2016 13:04 GMT, Sudheer Vinukonda <[email protected]> :

> Yes, I've seen the documentation about configuring the localnode
> setup.
>
> I still don't quite understand the lack of need for sync' ng states.
> I'm likely being naive about this, but, for the purpose of my
> clarification - 
>
> let's consider the case of non-localnode LVS cluster in load shared
> mode (similar to the setup described in the YouTube talk I shared in
> the original question).
>
> So, I've ECMP switch balancing requests between a set of LVS boxes,
> which are forwarding/balancing requests to a set of real servers
> behind them (say, using consistent hashing of the source address).
>
> If one of the LVS boxes went down, ECMP switch would redistribute the
> requests to the remaining LVS boxes. Even without syncing states, this
> is still fine, since any LVS box would still forward these requests to
> the correct real server based on the consistent hash. So far so good.
>
> Now, say, one of the real servers also went down. LVS on each box
> would now (recompute the hash and) forward requests meant for the down
> server to the remaining servers and record it's connection state on
> their respective state tables. Again, so far so good.
>
> Now, let's say both the LVS box and the real server that went down
> came back up. How will the just alive LVS forward the requests (for
> existing sessions) without knowing the state for them? Will it not end
> up sending them to the wrong real server (the server that just got
> alive) if it blindly uses the source hash, since it has no idea that
> this session was active/assigned to a different real server?

Yes, in this case, you need state syncing. However, in the local node
case, syncing is useless as a connection will not survive the switch as
the local TCP connection tables are different for each node.
-- 
Make sure every module hides something.
            - The Elements of Programming Style (Kernighan & Plauger)

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