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Ganeti Cluster tools (ganeti-htools)
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====================================
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**Note:** This document is obsolete and mostly documents the situation
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before the htools sources were integrated into the ganeti-core
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codebase. Information about the current situation is available in the
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``INSTALL`` file in the top-level directory.
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These are some simple cluster tools for fixing common allocation
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problems on Ganeti 2.0 clusters.
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Note that these tools are most useful for bigger cluster sizes
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(e.g. more than five or ten machines); at lower sizes, the computations
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they do can also be done manually.
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Most of the tools revolve around the concept of keeping the cluster N+1
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compliant: this means that in case of failure of any node, the instances
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affected can be failed over (via ``gnt-node failover`` or ``gnt-instance
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failover``) to their secondary node, and there is enough memory reserved
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for this operation without needing to shutdown other instances or
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rebalance the cluster.
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**Quick start** (see the installation section for more details):
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- (have the ghc compiler and the prerequisite libraries installed)
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- ``make``
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- ``./hbal -m $cluster -C -p``
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- look at the original and final cluster layout, and if acceptable,
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  execute the given commands
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Available tools
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---------------
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Cluster rebalancer
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~~~~~~~~~~~~~~~~~~
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The rebalancer uses a simple algorithm to try to get the nodes of the
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cluster as equal as possible in their resource usage. It tries to
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repeatedly move each instance one step, so that the cluster score
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becomes better. We stop when no further move can improve the score.
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For algorithm details and usage, see the man page ``hbal(1)``.
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IAllocator plugin
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~~~~~~~~~~~~~~~~~
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The ``hail`` iallocator plugin can be used for allocations of mirrored
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and non-mirrored instances and for relocations of mirrored instances. It
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needs to be installed in Ganeti's iallocator search path—usually
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``/usr/lib/ganeti/iallocators`` or
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``/usr/local/lib/ganeti/iallocators``, and after that it can be used via
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ganeti's ``--iallocator`` option (in various gnt-node/gnt-instance
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commands). See the man page ``hail(1)`` for more details.
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Cluster capacity estimator
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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The ``hspace`` program will, given an input instance specification,
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estimate how many instances of those type can be place on the cluster
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before it will become full (as in any new allocation would fail N+1
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checks). For more details, see the man page hspace(1).
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Integration with Ganeti
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-----------------------
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The ``hbal`` and ``hspace`` programs can either get their input from
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text files, locally from the master daemon (when run on the master node
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of a cluster), or remote from a cluster via RAPI. The "-L" argument
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enables local collection (with an optional path to the unix socket). For
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online collection via RAPI, the "-m" argument should specify the cluster
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or master node name. Only ``hbal`` and ``hspace`` use these arguments,
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``hail`` uses the standard iallocator API and thus doesn't need any
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special setup (just needs to be installed in the right directory).
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For generating the text files, a separate tool (``hscan``) is provided
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to automate their gathering if RAPI is available, which is better since
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it can extract more precise information. In case RAPI is not usable for
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whatever reason, ``gnt-node list`` and ``gnt-instance list`` could be
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used, and their output concatenated in a single file, separated by one
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blank line. If you need to do this manually, you'll need to check the
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sources to see which fields are needed exactly.
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The ``hail`` program gets its data automatically from Ganeti when used
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as described in its section.
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Installation
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------------
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If installing from source, you need a working ghc compiler (6.8 at
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least) and some extra Haskell libraries which usually need to be
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installed manually:
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- `json <http://hackage.haskell.org/package/json>`_
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- `curl <http://hackage.haskell.org/package/curl>`_
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- `network <http://hackage.haskell.org/package/network>`_
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- `parallel <http://hackage.haskell.org/package/parallel>`_, version 1.x
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Once these are installed, just typing *make* in the top-level directory
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should be enough. If you edit the documentation sources, you will need
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the ``pandoc`` program to rebuilt it.
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Only the ``hail`` program needs to be installed in a specific place, the
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other tools are not location-dependent.
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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``
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directory.
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.. vim: set textwidth=72 :
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.. Local Variables:
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.. mode: rst
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.. fill-column: 72
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.. End: