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.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 algorithm 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 considered 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.