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Hello all,

You may know that for deployment configuration we are serializing
additional prefix for controller role (primary), with the goal of
deployment order control (primary-controller always should be deployed
before secondaries) and some condiions in fuel-library code.

However, we cannot guarantee that primary controller will be always the
same node, because it is not business of nailgun to control elections of
primary. Essentially user should not rely on nailgun
information to find primary, but we need to persist node elected as primary
in first deployment
to resolve orchestration issues (when new node added to cluster we should
not mark it as primary).

So we called primary-controller - "internal" role, which means that it is
not exposed to users (or external developers).
But with introduction of plugins and granular deployment, in my opinion, we
need to be able
to specify that task should run specifically on primary, or on secondaries.
Alternative to this approach would be - always run task on all controllers,
and let task itself to verify that it is  executed on primary or not.

Is it possible to have significantly different sets of tasks for controller
and primary-controller?
And same goes for mongo, and i think we had primary for swift also.
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