[Pacemaker] need cluster-wide variables

Andrew Beekhof andrew at beekhof.net
Thu Jan 5 00:28:16 EST 2012

On Thu, Jan 5, 2012 at 3:59 PM, shashi <shashidhara.td at huawei.com> 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 not only do the Pre-masters need to behave differently, the Slaves
also need to know who the Pre-masters are.
Is that correct?

> 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.
> Thanks & Regards
> Shashi
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