Add a spec for ceph-ansible

Change-Id: I324c250e57125910b64fad6c06a4d68acf0600b4

specs/ceph-ansible.rst

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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+=================================
+Moving to ceph-ansible for Kolla
+=================================
+
+It has been discussed within the Kolla community that we should look at moving
+from our own orchestration and containers for Ceph to those provided by the
+'ceph-ansible' project. This spec proposes how this should happen.
+
+Problem description
+===================
+
+Ceph is a complex project that exists outside of OpenStack. As new versions of
+Ceph are released, the Kolla community have had to spend time and resources
+ensuring that our implementation is up to date, upgrade works correctly, etc,
+in addition to the multiple OpenStack services we support. Meanwhile, there are
+other existing projects that work just on Ceph, and can potentially do this
+much better.
+
+Use cases
+---------
+
+1. Ceph deployment using dedicated Storage nodes
+2. Ceph deployment using HCI nodes (storage nodes on compute nodes)
+
+Proposed change
+===============
+
+ceph-ansible is one such project that is part of the official Ceph
+project namespace[0]. This gives us a reasonable degree of certainty that it
+can provide a more complete and well maintained implementation of Ceph than
+Kolla can provide on its own.
+
+Alternatives
+------------
+
+Continue to maintain current approach i.e. Ceph deployment in kolla-ansible.
+
+Other End User impact
+---------------------
+
+We will need to move to images that ceph-ansible supports, we have two options:
+
+1. Directly use what is available on docker hub[1].
+2. Build images using ceph-container repo[2].
+
+NOTE: Currently ceph-container project does not support Ubuntu container images.
+
+Security impact
+---------------
+
+From a high level this should not have any security impact. It is possible
+security would be even improved over what we have now, due to the active
+community maintaining the ceph-ansible project[3].
+
+Performance Impact
+------------------
+
+We see no potential performance impact. The time for deploying ceph-ansible may
+end up being slightly longer or shorter when compared to Kolla's Ceph, but the
+difference should not be big.
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  mnasiadka
+
+Milestones
+----------
+
+Target Milestone for completion:
+  U
+
+Work Items
+----------
+
+1. Mark the current implementation of Ceph in Kolla as deprecated in the Train
+   cycle. The ceph-ansible implementation should be ready for the release of
+   U.
+
+2. Provide concise documentation on how a Kolla operator should go about
+   deploying ceph-ansible in a way that's consistent with Kolla best practices.
+
+3. Ensure we have a sensible and easy to follow upgrade path for those
+   currently running Kolla's implementation of Ceph in production.
+
+4. The current Kolla gates for Ceph will need to be updated.
+
+5. (Optional) Create a playbook for ceph-ansible integration - similar to the one OpenStack-Ansible
+   project has developed[4].
+
+Testing
+=======
+See work item number 4 above.
+
+Documentation Impact
+====================
+See work item number 2 above.
+
+References
+==========
+[0] http://docs.ceph.com/ceph-ansible/master/
+[1] https://hub.docker.com/r/ceph/daemon
+[2] https://github.com/ceph/ceph-container
+[3] https://github.com/ceph/ceph-ansible/graphs/contributors
+[4] https://opendev.org/openstack/openstack-ansible/src/branch/master/playbooks/ceph-install.yml