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Added doc for a affinity/anti-affinity

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Roman Dobosz
2017-12-11 15:20:02 -08:00
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commit e5aecce0cf
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specs/affinity-antiaffinity-of-instances-in-a-groups.rst Normal file
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===============================================
Affinity/Anti Affinity of instances in a groups
===============================================
This task can be divided into two separate parts. First is a change of behavior
of host aggregates, to be able to include ironic nodes. Second, involves
changes to the scheduler to support spreading instances across various groups.
Questions
---------
There are several ways that aggregate (anti)affinity could be defined
expressed.
#. Pass through hints, both information about server group and condition for
server placement against host aggregates:
.. code:: shell-session
openstack aggregate-create rack1
openstack aggregate-create rack2
openstack aggregate-set-metadata rack1 rack=1
openstack aggregate-set-metadata rack2 rack=1
openstack aggregate-add-host rack1 <UUID of Ironic node A>
openstack aggregate-add-host rack2 <UUID of Ironic node B>
openstack server-group-create not-same-rack anti-affinity
openstack server create --image=IMAGE_ID --flavor=1 \
--hint group=not-same-rack --hint property=rack
#. Implement own policies to set on instance groups, like
``rack_antiaffinity``, ``pz_antiaffinity`` etc, and than during boot time
just pass a server group name. For instance:
.. code:: shell-session
openstack aggregate-create rack1
openstack aggregate-create rack2
openstack aggregate-set-metadata rack1 rack=1
openstack aggregate-set-metadata rack2 rack=1
openstack aggregate-add-host rack1 <UUID of Ironic node A>
openstack aggregate-add-host rack2 <UUID of Ironic node B>
openstack server-group-create not-same-rack rack-anti-affinity
openstack server create --image=IMAGE_ID --flavor=1 \
--hint group=not-same-rack
#. Hardcode policy into the server group name, but this requires from users, to
be very strict about naming of server groups:
.. code:: shell-session
openstack aggregate-create rack1
openstack aggregate-create rack2
openstack aggregate-set-metadata rack1 rack=1
openstack aggregate-set-metadata rack2 rack=1
openstack aggregate-add-host rack1 <UUID of Ironic node A>
openstack aggregate-add-host rack2 <UUID of Ironic node B>
openstack server-group-create rack-<unique-name> anti-affinity
openstack server create --image=IMAGE_ID --flavor=1 \
--hint group=rack-<unique-name>
Which solution should we take?