Provided by: ganeti-htools_2.9.3-1_amd64 
NAME
hail - Ganeti IAllocator plugin
SYNOPSIS
hail [ -t file | --simulate spec ] [options...] input-file
hail --version
DESCRIPTION
hail is a Ganeti IAllocator plugin that implements the instance placement and movement 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.
If the input file name is - (a single minus sign), then the request data will be read from stdin.
ALGORITHM
The program uses a simplified version of the hbal algorithm.
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
algorithm is non-trivial with regard to cluster size.
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 node changes (change-node mode), we currently support DRBD instances only, and all three modes
(primary changes, secondary changes and all node changes).
For group moves (change-group mode), again only DRBD is supported, and we compute the correct sequence
that will result in a group change; job failure mid-way will result in a split instance. The choice of
node(s) on the target group is based on the group score, and the choice of group is based on the same
algorithm as allocations (group with lowest score after placement).
The deprecated multi-evacuate modes is no longer supported.
In all cases, the cluster (or group) scoring is identical to the hbal algorithm.
OPTIONS
The options that can be passed to the program are as follows:
-p, --print-nodes
Prints the before and after node status, in a format designed to allow the user to understand the
node's most important parameters. See the man page htools(1) for more details about this option.
-t datafile, --text-data=datafile
The name of the file holding cluster information, to override the data in the JSON request itself.
This is mostly used for debugging. The format of the file is described in the man page htools(1).
--simulate description
Backend specification: similar to the -t option, this allows overriding the cluster data with a
simulated cluster. For details about the description, see the man page htools(1).
-S filename, --save-cluster=filename
If given, the state of the cluster before and the iallocator run is saved to a file named
filename.pre-ialloc, respectively filename.post-ialloc. This allows re-feeding the cluster state
to any of the htools utilities via the -t option.
-v This option increases verbosity and can be used for debugging in order to understand how the
IAllocator request is parsed; it can be passed multiple times for successively more information.
CONFIGURATION
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 considered 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.
OPTIONS
The options that can be passed to the program are as follows:
EXIT STATUS
The exist status of the command will be zero, unless for some reason the algorithm fatally failed (e.g.
wrong node or instance data).
BUGS
Networks (as configured by gnt-network(8)) are not taken into account in Ganeti 2.7. The only way to
guarantee that they work correctly is having your networks connected to all nodegroups. This will be
fixed in a future version.
REPORTING BUGS
Report bugs to project website (http://code.google.com/p/ganeti/) or contact the developers using the
Ganeti mailing list (ganeti@googlegroups.com).
SEE ALSO
Ganeti overview and specifications: ganeti(7) (general overview), ganeti-os-interface(7) (guest OS
definitions), ganeti-extstorage-interface(7) (external storage providers).
Ganeti commands: gnt-cluster(8) (cluster-wide commands), gnt-job(8) (job-related commands), gnt-node(8)
(node-related commands), gnt-instance(8) (instance commands), gnt-os(8) (guest OS commands), gnt-
storage(8) (storage commands), gnt-group(8) (node group commands), gnt-backup(8) (instance import/export
commands), gnt-debug(8) (debug commands).
Ganeti daemons: ganeti-watcher(8) (automatic instance restarter), ganeti-cleaner(8) (job queue cleaner),
ganeti-noded(8) (node daemon), ganeti-masterd(8) (master daemon), ganeti-rapi(8) (remote API daemon).
Ganeti htools: htools(1) (generic binary), hbal(1) (cluster balancer), hspace(1) (capacity calculation),
hail(1) (IAllocator plugin), hscan(1) (data gatherer from remote clusters), hinfo(1) (cluster information
printer), mon-collector(7) (data collectors interface).
COPYRIGHT
Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 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.
Ganeti HAIL(1)