Commit ba83c4aa authored by Klaus Aehlig's avatar Klaus Aehlig

Extend location-awareness design by instance pinning

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: default avatarKlaus Aehlig <aehlig@google.com>
Reviewed-by: default avatarPetr Pudlak <pudlak@google.com>
parent 55f2627d
......@@ -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.
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