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Hello stackers,

In the pursuit to remove Mistral from the TripleO undercloud, we've
discovered an old capability that we need to figure out how best to handle.
Currently, we provide the ability for an end-user (operator / deployer) to
pass in "N" Mistral workflows as part of a given deployment plan which is
processed by python-tripleoclient at runtime [0][1]. From what we have
documented, and what we can find within the code-base, we're not using this
feature by default. That said, we do not remove something if it is
valuable in the field without an adequate replacement. The ability to run
arbitrary Mistral workflows at deployment time was first created in 2017
[2] and while present all this time, its documented [3] and intra-code-base
uses are still limited to samples [4]. As it stands now, we're on track to
making Mistral inert this cycle and if our progress holds over the next
couple of weeks the capability to run arbitrary Mistral workflows will be
the only thing left within our codebase that relies on Mistral running on
the Undercloud.

So the question is what do we do with functionality. Do we remove this
ability out right, do we convert the example workflow [5] into a
stand-alone Ansible playbook and change the workflow runner to an
arbitrary playbook runner, or do we simply leave everything as-is and
deprecate it to be removed within the next two releases? Although it would
be perfectly acceptable to keep Mistral around a little while longer, it
would also be a bummer if this one capability was the only reason we were
not able to remove Mistral from the Undercloud.

Any and all feedback from operators, deployers, developers, former
developers, etc would be greatly appreciated.

Thank you in advance.


[0]
https://opendev.org/openstack/python-tripleoclient/src/commit/af719b795bc9ba2b2c3dbcec855990ef815bfc2c/tripleoclient/workflows/parameters.py#L33-L74
[1]
https://opendev.org/openstack/python-tripleoclient/src/commit/af719b795bc9ba2b2c3dbcec855990ef815bfc2c/tripleoclient/v1/overcloud_deploy.py#L221-L224
[2] https://review.opendev.org/#/c/457874
[3]
https://specs.openstack.org/openstack/tripleo-specs/specs/pike/tripleo-derive-parameters.html
[4]
https://opendev.org/openstack/tripleo-heat-templates/src/commit/48da6a139367f21c4dfcd4afcbce1090cfc5f329/plan-samples/plan-environment-derived-params.yaml#L9
[5]
https://opendev.org/openstack/tripleo-common/src/commit/cc4f9c57b708259e9e946c6d0c45709b3ffaabe2/workbooks/derive_params.yaml


Kevin Carter
IRC: kecarter
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