Revision 25ee7fd8 doc/design-multi-reloc.rst

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to another group for policy reasons, or completely empty a given group
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to perform maintenance operations.
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To implement this, we propose a new ``multi-relocate`` IAllocator call


  		





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that will be able to compute inter-group instance moves, taking into


  		





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account mobility domains as appropriate. The interface proposed below


  		





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should be enough to cover the use cases mentioned above.


  		





  
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To implement this, we propose the addition of new IAllocator calls to


  		





  
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compute inter-group instance moves and group-aware node evacuation,


  		





  
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taking into account mobility domains as appropriate. The interface


  		





  
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proposed below should be enough to cover the use cases mentioned above.


  		





  
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With the implementation of this design proposal, the previous


  		





  
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``multi-evacuate`` mode will be deprecated.


  		





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.. _multi-reloc-detailed-design:


  		





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Detailed design


  		





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===============


  		





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We introduce a new ``multi-relocate`` IAllocator call whose input will


  		





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be a list of instances to move, and a "mode of operation" that will


  		





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determine what groups will be candidates to receive the new instances.


  		





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The mode of operation will be one of:


  		





  
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All requests honor the groups' ``alloc_policy`` attribute.


  		





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- *Stay in group*: the instances will be moved off their current nodes,


  		





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  but will stay in the same group; this is what the ``relocate`` call


  		





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  does, but here it can act on multiple instances. (Typically, the


  		





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  source nodes will be marked as drained, to avoid just exchanging


  		





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  instances among them.)


  		





  
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Changing instance's groups


  		





  
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--------------------------


  		





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- *Change group*: this mode accepts one extra parameter, a list of node


  		





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  group UUIDs; the instances will be moved away from their current


  		





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  group, to any of the groups in this list. If the list is empty, the


  		





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  request is, simply, "change group": the instances are placed in any


  		





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  group but their original one.


  		





  
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Takes a list of instances and a list of node group UUIDs; the instances


  		





  
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will be moved away from their current group, to any of the groups in the


  		





  
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target list. All instances need to have their primary node in the same


  		





  
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group, which may not be a target group. If the target group list is


  		





  
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empty, the request is simply "change group" and the instances are placed


  		





  
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in any group but their original one.


  		





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- *Any*: for each instance, any group is valid, including its current


  		





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  one.


  		





  
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Node evacuation


  		





  
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---------------


  		





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In all modes, the groups' ``alloc_policy`` attribute will be honored.


  		





  
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Evacuates instances off their primary nodes. The evacuation mode


  		





  
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can be given as ``primary-only``, ``secondary-only`` or


  		





  
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``all``. The call is given a list of instances whose primary nodes need


  		





  
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to be in the same node group. The returned nodes need to be in the same


  		





  
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group as the original primary node.


  		





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.. _multi-reloc-result:


  		





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(when shared storage is used, they will all be failover or migration


  		





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operations within the corresponding mobility domain).


  		





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The result is expected to be a list of jobsets. Each jobset contains


  		





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lists of serialized opcodes. Example::


  		





  
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The result of the operations described above must contain two lists of


  		





  
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instances and a list of jobsets.


  		





  
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The two lists of instances describe which instances could be


  		





  
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moved/migrated and which couldn't for some reason ("unsuccessful"). The


  		





  
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union of the two lists must be equal to the set of instances given in


  		





  
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the original request.


  		





  
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The list of jobsets contained in the result describe how to actually


  		





  
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execute the operation. Each jobset contains lists of serialized opcodes.


  		





  
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Example::


  		





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  [


  		





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    [


  		





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Starting with the first set, Ganeti will submit all jobs of a set at the


  		





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same time, enabling execution in parallel. Upon completion of all jobs


  		





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in a set, the process is repeated for the next one. Ganeti is at liberty


  		





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to abort the execution of the relocation after any jobset. In such a


  		





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case the user is notified and can restart the relocation.


  		





  
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to abort the execution after any jobset. In such a case the user is


  		





  
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notified and can restart the operation.


  		





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