Synnefo » snf-ganeti » ganeti-local

Ganeti Cluster tools (ganeti-htools)

====================================

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.

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).

Cluster N+1 solver

~~~~~~~~~~~~~~~~~~

This program runs a very simple brute force algorithm over the instance

placement space in order to determine the shortest number of replace-disks

needed to fix the cluster. Note this means we won't get a balanced cluster,

just one that passes N+1 checks.

For algorithm details and usage, see the man page hn1(1).

.. note:: This program is deprecated, hbal should be used instead.

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``. See the man page hail(1).

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 ``hn1`` programs can either get their input from text

files, or online from a cluster via RAPI. For online collection via

RAPI, the "-m" argument to both hn1 and hbal should specify the

cluster or master node name. ``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, the following two commands should be run::

    gnt-node list -oname,mtotal,mnode,mfree,dtotal,dfree,offline \

      --separator '|' --no-headers > nodes

    gnt-instance list -oname,be/memory,sda_size,status,pnode,snodes \

      --separator '|' --no-head > instances

These two files should be saved under the names of *nodes* and

*instances*.

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

- curl

Once these are available, just typing *make* in the top-level

directory should be enough.

Internal (implementation) documentation is available in the ``apidoc``

directory.

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