It is a frequent request to be able to specify desired locations for particular instances. Describe a tag-based way of achieving this without adding hard enforcements.
Signed-off-by: Klaus Aehlig <[email protected]> --- doc/design-location.rst | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/doc/design-location.rst b/doc/design-location.rst index 9d0f7aa..55aa228 100644 --- a/doc/design-location.rst +++ b/doc/design-location.rst @@ -109,3 +109,21 @@ Advise only These tags are of advisory nature only. That is, all ``htools`` will strictly obey the restrictions imposed by those tags, but Ganeti will not prevent users from manually instructing other migrations. + + +Instance pinning +================ + +Sometimes, administrators want specific instances located in a particular, +typically geographic, location. To support these kind of requests, instances +can be assigned tags of the form *htools:desiredlocation:x* where *x* is a +failure tag. Those tags indicate the the instance wants to be placed on a +node tagged *x*. To make ``htools`` honor those desires, the metric is extended, +appropriately weighted, by the following component. + +- The number of instances tagged *htools:desiredlocation:x* where their + primary node is not tagged with *x*. + +Again, instance pinning is just heuristics, not a hard enforced requirement; +it will only be achieved by the cluster metrics favouring such placements. + -- 2.4.3.573.g4eafbef
