SchedulerHintsAPI

The Nova API for instance creation supports a scheduler_hints mechanism whereby the user can pass additional placement related information into the Nova scheduler.

The implementation of scheduler_hints lies (mostly) in the various scheduler filters, and the set of hints which are supported on any system therefore depends on the filters that have been configured (this could include non-standard filters). It is therefore not currently possible for a user of the system to determine which hints are available. Hints that are not supported will be silently ignored by the scheduler

As new filters are added more and more hints are becoming potentially available.

Current examples include: From the scheduler itself: group Affinity filter: same_host, cidr, different_host JSON filer: query

A simple option would be to provide an API which lists the filters and weighting functions configured for the scheduler (c.f. querying API extensions), and rely on filter documentation to describe the supported hints,

A more comprehensive solution would be to make each filter / weighting function would provide a query that returns a description of its supported hints. The novaclient could then provide the list of supported hints in its help screens.