Orchestrating a patch installation scenario in a application sever cluster

[Denis Weerasiri]

Hi,
I am trying to realize the following patch installation scenario in a
application cluster fronted with a load-balancer.
Let's assume I use Puppet like a configuration management tool to install
the patch in each node.

Here is the scenario

   - The cluster is consist of two nodes named A and B.
   - First stop the node A and install the patch using a puppet manifest
   and restart the node A
   - Then stop the node B and install the patch using a puppet manifest and
   restart the node B
   - So the application is available 100% at all the times

The problem is, how can I write a charm to automate this patch installation
scenario, where *Juju should be able to propagate life-cycle changes in one
service unit in Node A to the other service unit in Node B*.
When I went through the Juju doc, I found about subordinate services which
may solve my problem https://juju.ubuntu.com/docs/subordinate-services.html .
Is this the correct way of automating this patch installation scenario?
Or how is it possible to propagate life-cycle changes in one service unit
to the another service unit?



-- 
Thanks,
Denis
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*Denis Weerasiri*
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