Having an instance and an attached volume on the same physical host
(i.e. data locality) can be desirable in some configurations, in order
to achieve high-performance disk I/O.
This patch adds an InstanceLocalityFilter filter that allow users to
request creation of volumes 'local' to an existing instance, without
specifying the hypervisor's hostname, and without any knowledge of the
underlying back-ends.
In order to work:
- At least one physical host should run both nova-compute and
cinder-volume services.
- The Extended Server Attributes extension needs to be active in Nova
(this is by default), so that the 'OS-EXT-SRV-ATTR:host' property is
returned when requesting instance info.
- The user making the call needs to have sufficient rights for the
property to be returned by Nova. This can be achieved either by
changing Nova's policy.json (the 'extended_server_attributes' option),
or by setting an account with privileged rights in Cinder conf.
For example:
Instance 01234567-89ab-cdef is running in a hypervisor on the physical
host 'my-host'.
To create a 42 GB volume in a back-end hosted by 'my-host':
cinder create --hint local_to_instance=01234567-89ab-cdef 42
Note:
Currently it is not recommended to allow instance migrations for
hypervisors where this hint will be used. In case of instance
migration, a previously locally-created volume will not be
automatically migrated. Also in case of instance migration during the
volume's scheduling, the result is unpredictable.
DocImpact: New Cinder scheduler filter
Change-Id: Id428fa2132c1afed424443083645787ee3cb0399
0269a26f13