.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\(hyfile containing current cluster
state and the request details, and output (on stdout) a JSON\(hyformatted
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\(hynode allocations (non\(hymirrored instances), again we
select the node which, when chosen as the primary node, gives the best
score.

For dual\(hynode allocations (mirrored instances), we chose the best
pair; this is the only choice where the algoritm is non\(hytrivial
with regard to cluster size.

For node evacuations (\fImulti-evacuate\fR 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.

.SH 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 \fBhtools:iextags:\fR

- use their suffix as the prefix for exclusion tags

For example, given a cluster tag like \fBhtools:iextags:service\fR,
all instance tags of the form \fBservice:X\fR will be confidered as
exclusion tags, meaning that (e.g.) two instances which both have a
tag \fBservice:foo\fR will not be placed on the same primary node.

.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 hbal "(1), " hspace "(1), " hscan "(1), " ganeti "(7), "
.BR gnt-instance "(8), " 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.