[Pacemaker] master/slave or unique clones

Vadym Chepkov vchepkov at gmail.com
Fri May 28 11:51:16 EDT 2010

On May 28, 2010, at 11:17 AM, Florian Haas wrote:

> On 05/28/2010 02:37 PM, Vadym Chepkov wrote:
>> On May 28, 2010, at 8:27 AM, Florian Haas wrote:
>>>> Imperative word was "started". You think I still should go multi-state RA for this application?
>>> If the application which that RA applies to distinguishes between roles
>>> equivalent to a Master and a Slave, and you want the RA to manage those,
>>> then probably yes.
>>> What makes you think you can't start the RA in Slave mode?
>> Because when application starts and able do bind to "master" ip it becomes master right away, there is no way to promote or demote.
>> Should I fake it in RA?
> Perhaps you could share just what you're trying to achieve, for what
> application, and how from the application's point of view the master is
> different from the slave?  I understand that you have this all laid out
> in your head, but the information you've given here is very sparse. This
> makes it hard to follow, and difficult to give advice. It's a bit like
> discussing the view of a beautiful landscape with blindfolds on. :)

I am sorry I wasn't informative before, I will try again

>> I want to convert our home-made application to be managed by pacemaker cluster. 
>> The way it works now: application starts, discovers all IPs configured on the system and if it sees preconfigured IP it becomes "master" and will serve configuration requests, 
>> if not - "node" and will try to connect to "master" node to get configuration data. Other then that, application instances are absolutely the same on all "cluster" servers and 
>> they start collecting their own unique data.

So, application acts as "master" if it was able to bind to the pre-configured IP and as a "node" if it wasn't. If it's a master it listens on an additional port and receives updates from nodes. Each application pulls video feed out of attached video cameras and stores them on the local drives, that what makes them unique.

What I want to achieve:

1. Have "master" IP running on one of the 2 servers (attached to shared EMC storage)
2. Have "master" app started on "master" IP and insure it's running.
3. Start application on each node and make sure it's running.

Hopefully this clears the landscape a bit :)

Appreciate your help.

Vadym Chepkov

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