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Hi Gerd,
On Wed, Sep 02, 2009 at 11:52:17PM +0200, it-intuition wrote:
> Hello,
>
> we are currently using lvs for balancing two webservers by using the wrr
> scheduler in combination with persistance.
> Now we want to modify our setup to use one primary webserver and a
> secondary webserver as a backup server. My idea was to set the weight of
> the primary webserver to 1000 and for the backup server to 0.
>
> These are the question that came up in my mind:
>
> 1. How will this setup behave if the primary webserver is down?
I suspect all connections will fail.
> 2. How will this setup behave if the primary webserver is up again?
As it did before the primary went down.
>
> 3. Does a weight of 0 mean, that no connection to the backup server can
> be made (if the primary webserver is down)?
A real-server with a weight of 0 won't get any new connections, unless they
are associated with a recent connection and the service is marked as
persistent.
In your case, this should mean no, no connections will be sent
to the backup server.
In short I think the basic effect of this setup would be the
same as not having the backup server in the pool at all.
> The last question may sound stupid, but I read that a weight of 0 is
> often used to silently take a server out of a pool.
> So I think a weight of 0 prevents clients to connect; which is not the
> effect I want for our setup.
>
> Any help or comments would be appreciated.
I think that a better strategy is to have a higher level monitor
looking at your servers and inserting the backup server into lvs
as needed. ldirectord and keepalived should both be able to do this.
Alternatively, explicit support for this kind of backup server arrangement
could be added to lvs. But it would rely on a fairly low-level view of
weather the primary is up or down.
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