add force detach to nova

Change-Id: Ic4f9a0b3e2443db7852e8c5c18ce37584dff6943

specs/juno/add-force-detach-to-nova.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
+
+=================================================================
+Add force detach to nova
+=================================================================
+
+https://blueprints.launchpad.net/nova/+spec/add-force-detach-to-nova
+
+Add force detach to nova for cleaning the attach information in nova,
+and make it better than only calling "force detach" in cinder like 
+attach and detach.
+
+Problem description
+====================
+
+There is use case: we have two nova components（call them nova A and nova B） 
+and one cinder component. Attach a volume to an instance in nova A and then 
+services of nova A become abnormal. Because the volume also want to be used 
+in nova B, so using cinder api "force detach volume" to free this volume. 
+But when nova A is normal, nova can't detach this volume from instance by 
+using nova api "detach volume", as nova check the volume state must be 
+"attached".
+
+proposed change
+================
+
+1. Add optional "force_detach" parameter which is boolean variable 
+(default value is false) in nova detach api.
+
+2. When force_detach is true, nova will detach the volume for clean the attach information 
+whether volume status is attached or detached.
+
+3. Then call force detach api in cinder.
+		
+
+
+Alternatives
+-------------
+
+None
+
+Data model impact
+------------------
+
+None
+
+REST API impact
+----------------
+
+Add an optional parameter "force_detach=true/false" 
+in rest body of nova detach api. 
+
+Security Impact
+---------------
+
+None
+
+Notifications impact
+---------------------
+
+None
+
+Other End user impact
+-----------------------
+
+None
+
+Performance  Impact
+---------------------
+
+There is no impact about the performance of nova.
+
+Deployer impact 
+----------------
+
+None
+
+Developer impact
+----------------
+
+None
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Assignee: wanghao749 <wanghao749@huawei.com>
+
+
+Work Items
+----------
+
+None
+
+
+Dependencies
+============
+
+None
+
+
+Testing
+=======
+
+Unit tests and tempest tests will check "force detach" function.
+
+
+Documentation Impact
+====================
+
+A description of this function will be added into Compute API V2 Reference.
+
+
+References
+==========
+
+None