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Ganeti Cluster tools (ganeti-htools)
====================================

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**Note:** This document is obsolete and mostly documents the situation
before the htools sources were integrated into the ganeti-core
codebase. Information about the current situation is available in the
``INSTALL`` file in the top-level directory.

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These are some simple cluster tools for fixing common allocation
problems on Ganeti 2.0 clusters.

Note that these tools are most useful for bigger cluster sizes
(e.g. more than five or ten machines); at lower sizes, the computations
they do can also be done manually.

Most of the tools revolve around the concept of keeping the cluster N+1
compliant: this means that in case of failure of any node, the instances
affected can be failed over (via ``gnt-node failover`` or ``gnt-instance
failover``) to their secondary node, and there is enough memory reserved
for this operation without needing to shutdown other instances or
rebalance the cluster.

**Quick start** (see the installation section for more details):

- (have the ghc compiler and the prerequisite libraries installed)
- ``make``
- ``./hbal -m $cluster -C -p``
- look at the original and final cluster layout, and if acceptable,
  execute the given commands


Available tools
---------------

Cluster rebalancer
~~~~~~~~~~~~~~~~~~

The rebalancer uses a simple algorithm to try to get the nodes of the
cluster as equal as possible in their resource usage. It tries to
repeatedly move each instance one step, so that the cluster score
becomes better. We stop when no further move can improve the score.

For algorithm details and usage, see the man page ``hbal(1)``.

IAllocator plugin
~~~~~~~~~~~~~~~~~

The ``hail`` iallocator plugin can be used for allocations of mirrored
and non-mirrored instances and for relocations of mirrored instances. It
needs to be installed in Ganeti's iallocator search path—usually
``/usr/lib/ganeti/iallocators`` or
``/usr/local/lib/ganeti/iallocators``, and after that it can be used via
ganeti's ``--iallocator`` option (in various gnt-node/gnt-instance
commands). See the man page ``hail(1)`` for more details.

Cluster capacity estimator
~~~~~~~~~~~~~~~~~~~~~~~~~~

The ``hspace`` program will, given an input instance specification,
estimate how many instances of those type can be place on the cluster
before it will become full (as in any new allocation would fail N+1
checks). For more details, see the man page hspace(1).


Integration with Ganeti
-----------------------

The ``hbal`` and ``hspace`` programs can either get their input from
text files, locally from the master daemon (when run on the master node
of a cluster), or remote from a cluster via RAPI. The "-L" argument
enables local collection (with an optional path to the unix socket). For
online collection via RAPI, the "-m" argument should specify the cluster
or master node name. Only ``hbal`` and ``hspace`` use these arguments,
``hail`` uses the standard iallocator API and thus doesn't need any
special setup (just needs to be installed in the right directory).

For generating the text files, a separate tool (``hscan``) is provided
to automate their gathering if RAPI is available, which is better since
it can extract more precise information. In case RAPI is not usable for
whatever reason, ``gnt-node list`` and ``gnt-instance list`` could be
used, and their output concatenated in a single file, separated by one
blank line. If you need to do this manually, you'll need to check the
sources to see which fields are needed exactly.


The ``hail`` program gets its data automatically from Ganeti when used
as described in its section.

Installation
------------

If installing from source, you need a working ghc compiler (6.8 at
least) and some extra Haskell libraries which usually need to be
installed manually:

- `json <http://hackage.haskell.org/package/json>`_
- `curl <http://hackage.haskell.org/package/curl>`_
- `network <http://hackage.haskell.org/package/network>`_
- `parallel <http://hackage.haskell.org/package/parallel>`_, version 1.x

Once these are installed, just typing *make* in the top-level directory
should be enough. If you edit the documentation sources, you will need
the ``pandoc`` program to rebuilt it.

Only the ``hail`` program needs to be installed in a specific place, the
other tools are not location-dependent.

For running the (admittedly small) unittest suite (via *make check*),
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the QuickCheck version 2 library is needed.
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Internal (implementation) documentation is available in the ``apidoc``
directory.

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