[ClusterLabs] Antw: Interacting with Pacemaker from my code

Nishant Nakate technonsquare at gmail.com
Tue Jul 16 02:58:51 EDT 2019

On Tue, Jul 16, 2019 at 11:33 AM Ulrich Windl <
Ulrich.Windl at rz.uni-regensburg.de> wrote:

> >>> Nishant Nakate <technonsquare at gmail.com> schrieb am 16.07.2019 um
> 05:37 in
> Nachricht
> <CANTAVSkfNnx=ZQv+UftaKs76Htk3VU+kO=bqHrOj4ssZx+Ou4A at mail.gmail.com>:
> > Hi All,
> >
> > I am new to this community and HA tools. Need some guidance on my current
> > handling pacemaker.
> >
> > For one of my projects, I am using pacekmaker for high availability.
> > Following the instructions provided in setup document, I am able to
> create
> > a new cluster with three nodes. Tested the failover and it works as
> > expected. Now, I need to run our own code on this nodes. I am going to
> use
> > Active-Pasive topology for our system architecture.
> >
> > I would like to know, how can I detect from my code if DC has changed ?
> So
> > that tools running on new DC can take over the controll of application
> > logic.
> Why would you need that? crm_mon shows where ther DC is.
> Thanks you Ulrich for your quick response.

I will give you a quick overview of the system. There would be 3 nodes
configured in a cluster. One would act as a leader and others as followers.
Our system would be actively running on all the three nodes and serve
external services assigned to them. On top of that, the Leader would have
some services running. In case the leader node (DC) fails, load of failed
leader needs to be distributed among followers. One should get elected as
next leader and start the additional services the previous leader was

In this case, a our system daemon running on the next node (designated as
new coordinater) needs to know that DC has changed and start the additional
services. Hope this clarifies my need.

AFAIK, crm_mon (or dcs) needs to be run from command line. Are you
suggesting that I create a service which runs crm_mon and parse the ourput
in a loop to check changes in DC/resources ?

> > Also, how to configure my processes (tools) as resources so that
> Pacemaker
> > can make them HA.
> You'll have to write an RA (resource agent) at least, but more importantly
> the application has the be designed for HA to be effective.
We are currently designing the services which are all stateless. If you
have any quick suggestions to be considered, please let me know. Also, what
type of RA would be helpful in this case. My services would be written in

> >
> > Please let me know if you need any clarification or any other
> information.
> >
> > Thanks in advance !!!
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