.TH HAIL 1 2009-03-23 htools "Ganeti H-tools"
.SH NAME
hail \- Ganeti IAllocator plugin

.SH SYNOPSIS
.B hail
.I "input-file"

.B hail
.B --version

.SH DESCRIPTION
hail is a Ganeti IAllocator plugin that allows automatic instance
placement and automatic instance secondary node replacement using the
same algorithm as \fBhbal\fR(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.

.SS ALGORITHM

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 all choices, the cluster scoring is identical to the hbal
algorithm.

.SH 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).

.SH SEE ALSO
.BR hn1 "(1), " hscan "(1), " ganeti "(7), " gnt-instance "(8), "
.BR gnt-node "(8)"

.SH "COPYRIGHT"
.PP
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.
.PP
On Debian systems, the complete text of the GNU General Public License
can be found in /usr/share/common-licenses/GPL.