Merge "Migrate stack to convergence engine"

specs/newton/convergence-migrate-stacks.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
+
+========================================================
+Operator Tool to migrate stacks to the convergence mode.
+========================================================
+
+https://blueprints.launchpad.net/heat/+spec/convergence-migrate-stack
+
+It would be useful for operators to make sure all stacks are being run
+under the same logic in order to support the service better.
+
+Problem description
+===================
+
+Whether or not a stack action is run under convergence is sticky,
+meaning that if the current "convergence_engine" setting is True when
+the stack-create is run, then that stack will always be run with the
+convergence logic (the same is also true for convergence_engine=False).
+
+Proposed change
+===============
+
+This spec proposes a new tool for operators that migrates any stack created
+under the legacy mode to convergence mode.
+
+This will only convert stack that are in a sane state (\*_COMPLETE) and
+will warn the operator if they need to re-run the command to catch
+stacks currently have actions in progress.
+
+The steps the operator will need to take are:
+
+1. edit /etc/heat/heat.conf change convergence_engine to what they want
+2. restart heat-engine
+3. run "heat-manage migrate-convergence-1 <stack_id>"
+
+
+Alternatives
+------------
+
+1. Stacks could be left to run in both modes and eventually users would
+   re-create stacks thus migrating them to the new mode (this could take
+   a long time though).
+2. We could automatically convert stacks on the next
+   stack-update. This takes the control out of the operators hands,
+   but has the advantage of doing this operation piecemeal and the
+   end-user could fix any issues that arise. (asalkeld: I think this could be
+   an attractive option).
+3. Grow some balls and decide that we are going with convergence and
+   make this a migration script (aka no-going-back).
+
+Implementation
+==============
+
+Extend *heat-manage* as follows::
+
+    heat-manage migrate-convergence-1 <stack_id>
+
+This command will call code in stack.py to get stack with stack_id and
+all it nested stuff. We need to set convergence = True,
+prev_raw_template_id = None and remove appropriate raw template,
+generate and add new traversal_id and set current_template_id for all
+resources in these stacks.
+Also we need to fill `needed_by` and `requires` columns in the database
+with corresponding dependencies.
+
+Assignee(s)
+-----------
+
+Primary assignee:
+   ochuprykov
+
+
+Milestones
+----------
+
+Target Milestone for completion:
+  newton-2
+
+Work Items
+----------
+
+- add the new command to heat-manage.
+- add code to stack.py to do the migration.
+- unit tests.
+- functional tests: https://review.openstack.org/#/c/230292/
+
+Dependencies
+============
+
+None