Re: MirrorMode behind fail over loadbalancer

[Gavin Henry <ghenry@suretecsystems.com>]

Diaa Radwan wrote:
> We have two openldap 2.4.7 , configured as MirrorMode, We are planning
> to add load balancer in front of both servers into the production
> environment, We don't want too go through conflicts issues as it was
> stated before as messy process.
>
>
> ---------	---------
> .	.	.	.	
> .  Srv1	.	.  Srv2	.
> ---------	---------		
>    \                 /
>     ---- ------------
>        . LoadB   .
> 	.-------.
>
> As per my understanding, the load balancer(failover mode) is
> redirecting all traffic to the active server(srv1); if the active
> server went down the traffic will be redirected to stand-by
> server(srv2). When srv1 goes online again the load balancer will
> redirect all trafic to srv1, while srv1 is in progress to get synced
> with srv2. The load balancer will not consider the sync process; it
> will just redirect the traffic.
>
> it was previously stated on the mailing list that there should be one
> write at a time. is there any conflict will occur when server getting
> bulk syncing and receiving updates(attribute level)/add requests as
> well?
>
> What happen if there attribute-level conflict? how to avoid it?
> suggestions are highly welcomed.

I would recommend the LB only redirects when the server it is 
*currently* pointing to goes down.

That way, if svr1 goes down, svr2 becomes active. When svr1 comes back, 
it resynchronises and is ready and waiting to take over should svr2 go down.

If you immediately switch and you have some hardware failure that has 
caused corruptions or other things on svr1, then it would be unwise for 
that to become the active node until you have fully investigated why it 
went down in the first place.

Gavin.

--
Kind Regards,

Gavin Henry.
Managing Director.

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