[Pacemaker] need cluster-wide variables

Dejan Muhamedagic dejanmm at fastmail.fm
Tue Jan 10 14:08:50 EST 2012


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 & Regards
> Shashi
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