[Pacemaker] need cluster-wide variables

[Dejan Muhamedagic]

Hi,

On Thu, Jan 05, 2012 at 04:59:13AM +0000, shashi wrote:
> > Its not something we had planned, this is the first time anyone has asked.
> > I'd be happy to help point someone on your side in the right
> > direction, but if I have to do all of it, you might be waiting a
> > while.
> > 
> > Can you explain the use case further?  Maybe there is another option.
> > 
> 
> Here is our scenario:
> We have a stateful(tri-state) service. (Master, Preferred Master, Slave).
> We want to achieve a tree like structure where in root node is master and leaf 
> nodes are slaves and the in-between nodes are Preferred Masters (There could 
> be more than one preferred master. (Basically this is done to reduce the load 
> from the Master, Otherwise all Slaves need to synchronize from Master).
> 
>               Master
>               /    \
>       Pre-Master   Pre-Master
>      /       |        \
> Slave     Slave       Slave
> 
> Master synchronizes its data with the attached Preferred Masters and Slaves 
> synchronizes its data from attached Prefered Master. 
> We want one of the Pre-Master to take over as master in case of master 
> instance failure (simultaneously tree restructuring is required) and one of 
> the slave to take over the Pre-Master role when one of the Pre-Master Fails.
> 
> So we have two probable options:
> 1. An work around to achieve this tri-state efficiently without changing 
> pacemaker internals.
> 2. Modify pacemaker to add this tri-state feature.
> 
> So please suggest how to go about it.

This sounds too complex to me. And it won't scale (if there are
too many Pre-Masters you may want to introduce Pre-Pre-Masters).
How about moving the logic to slaves, i.e. that they figure out
themselves which master to connect to? This is of course
oversimplification, but I'd rather try that way.

Thanks,

Dejan

> Thanks & Regards
> Shashi
> 
> 
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