hail - Ganeti IAllocator plugin
hail is a Ganeti IAllocator plugin that allows automatic instance
placement and automatic instance secondary node replacement using the
same algorithm as hbal(1).
The program takes input via a JSON‐file containing current cluster
state and the request details, and output (on stdout) a JSON‐formatted
response. In case of critical failures, the error message is printed on
stderr and the exit code is changed to show failure.
The program uses a simplified version of the hbal algorithm.
For relocations, we try to change the secondary node of the instance to
all the valid other nodes; the node which results in the best cluster
score is chosen.
For single‐node allocations (non‐mirrored instances), again we select
the node which, when chosen as the primary node, gives the best score.
For dual‐node allocations (mirrored instances), we chose the best pair;
this is the only choice where the algoritm is non‐trivial with regard
to cluster size.
For node evacuations (multi-evacuate mode), we iterate over all
instances which live as secondaries on those nodes and try to relocate
them using the single-instance relocation algorithm.
In all cases, the cluster scoring is identical to the hbal algorithm.
For the tag-exclusion configuration (see the manpage of hbal for more
details), the list of which instance tags to consider as exclusion tags
will be read from the cluster tags, configured as follows:
- get all cluster tags starting with htools:iextags:
- use their suffix as the prefix for exclusion tags
For example, given a cluster tag like htools:iextags:service, all
instance tags of the form service:X will be confidered as exclusion
tags, meaning that (e.g.) two instances which both have a tag
service:foo will not be placed on the same primary node.
The exist status of the command will be zero, unless for some reason
the algorithm fatally failed (e.g. wrong node or instance data).
hbal(1), hspace(1), hscan(1), ganeti(7), gnt-instance(8), gnt-node(8)
Copyright (C) 2009 Google Inc. Permission is granted to copy,
distribute and/or modify under the terms of the GNU General Public
License as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
On Debian systems, the complete text of the GNU General Public License
can be found in /usr/share/common-licenses/GPL.