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HAIL(1) Ganeti | Version @GANETI_VERSION@

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NAME

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hail - Ganeti IAllocator plugin

SYNOPSIS

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**hail** [ **-t** *file* | **--simulate** *spec* ] [options...] *input-file*

**hail** --version

DESCRIPTION

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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.

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 algorithm 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.

OPTIONS

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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 **hbal**(1) for more details about this

  field.

-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.

--simulate *description*

  Similar to the **-t** option, this allows overriding the cluster

  data with a simulated cluster. For details about the description,

  see the man page **hspace**(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.

-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

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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

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The exist status of the command will be zero, unless for some reason

the algorithm fatally failed (e.g. wrong node or instance data).

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