Merge "Introduce Glance Taskflow stopfile feature"

specs/pike/approved/glance/lite-specs.rst

@@ -133,5 +133,37 @@ Introduce db sync --check feature
 End of `Introduce db sync --check feature`
 ++++++++++++++++++++++++++++++++++++++++++
 
+Introduce Glance Taskflow stopfile feature
+------------------------------------------
+
+:problem: When preparing to take a Glance node down for maintenance or upgrade
+          it is necessary to allow long-running operations to complete without
+          allowing new operations to begin. The Taskflow engine does not have
+          the capability to prevent individual executors from starting new
+          jobs, and so attempting to take a Glance node out of the Taskflow
+          processing pool risks a race condition with that executor starting a
+          job just before the service is terminated which could cause the Task
+          processing to fail.
+
+:solution: Introduce a disable_by_file_path feature to Glance Taskflow which
+           will prevent the node from picking up new jobs. This allows an
+           operator or automation engine to ``touch`` the appropriate file
+           before terminating the service. This feature should depend on the
+           oslo healthcheck middleware configuration to disable the taskflow
+           engine. As an additional impact, this work will require Glance to
+           instantiate a single taskflow engine as a singleton and reuse that
+           engine instance on all subsequent taskflow operations.
+
+:impacts: None
+
+:timeline: Expected to have a fix merged in the Pike cycle before milestone 2.
+
+:link: https://docs.openstack.org/developer/oslo.middleware/healthcheck_plugins.html
+
+:assignee: Unknown
+
+End of `Introduce Glance Taskflow stopfile feature`
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+
 Add your Spec Lite before this line
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