Commit ffa6869f authored by Iustin Pop's avatar Iustin Pop

Convert the admin guide to restructured text

The RST format holds a little bit less information, as all the <file
class="directory"> and <userinput> tags are gone, however we're not
really losing important context here. And it's way easier to read and
update.

Reviewed-by: imsnah
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Ganeti administrator's guide
============================
Documents Ganeti version 2.0
.. contents::
Introduction
------------
Ganeti is a virtualization cluster management software. You are
expected to be a system administrator familiar with your Linux
distribution and the Xen or KVM virtualization environments before
using it.
The various components of Ganeti all have man pages and interactive
help. This manual though will help you getting familiar with the
system by explaining the most common operations, grouped by related
use.
After a terminology glossary and a section on the prerequisites needed
to use this manual, the rest of this document is divided in three main
sections, which group different features of Ganeti:
- Instance Management
- High Availability Features
- Debugging Features
Ganeti terminology
~~~~~~~~~~~~~~~~~~
This section provides a small introduction to Ganeti terminology,
which might be useful to read the rest of the document.
Cluster
A set of machines (nodes) that cooperate to offer a coherent
highly available virtualization service.
Node
A physical machine which is member of a cluster.
Nodes are the basic cluster infrastructure, and are
not fault tolerant.
Master node
The node which controls the Cluster, from which all
Ganeti commands must be given.
Instance
A virtual machine which runs on a cluster. It can be a
fault tolerant highly available entity.
Pool
A pool is a set of clusters sharing the same network.
Meta-Cluster
Anything that concerns more than one cluster.
Prerequisites
~~~~~~~~~~~~~
You need to have your Ganeti cluster installed and configured before
you try any of the commands in this document. Please follow the
*Ganeti installation tutorial* for instructions on how to do that.
Managing Instances
------------------
Adding/Removing an instance
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Adding a new virtual instance to your Ganeti cluster is really easy.
The command is::
gnt-instance add \
-n TARGET_NODE:SECONDARY_NODE -o OS_TYPE -t DISK_TEMPLATE \
INSTANCE_NAME
The instance name must be resolvable (e.g. exist in DNS) and usually
to an address in the same subnet as the cluster itself. Options you
can give to this command include:
- The disk size (``-s``) for a single-disk instance, or multiple
``--disk N:size=SIZE`` options for multi-instance disks
- The memory size (``-B memory``)
- The number of virtual CPUs (``-B vcpus``)
- Arguments for the NICs of the instance; by default, a single-NIC
instance is created. The IP and/or bridge of the NIC can be changed
via ``--nic 0:ip=IP,bridge=BRIDGE``
There are four types of disk template you can choose from:
diskless
The instance has no disks. Only used for special purpouse operating
systems or for testing.
file
The instance will use plain files as backend for its disks. No
redundancy is provided, and this is somewhat more difficult to
configure for high performance.
plain
The instance will use LVM devices as backend for its disks. No
redundancy is provided.
drbd
.. note:: This is only valid for multi-node clusters using DRBD 8.0.x
A mirror is set between the local node and a remote one, which must
be specified with the second value of the --node option. Use this
option to obtain a highly available instance that can be failed over
to a remote node should the primary one fail.
For example if you want to create an highly available instance use the
drbd disk templates::
gnt-instance add -n TARGET_NODE:SECONDARY_NODE -o OS_TYPE -t drbd \
INSTANCE_NAME
To know which operating systems your cluster supports you can use
the command::
gnt-os list
Removing an instance is even easier than creating one. This operation
is irrereversible and destroys all the contents of your instance. Use
with care::
gnt-instance remove INSTANCE_NAME
Starting/Stopping an instance
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Instances are automatically started at instance creation time. To
manually start one which is currently stopped you can run::
gnt-instance startup INSTANCE_NAME
While the command to stop one is::
gnt-instance shutdown INSTANCE_NAME
The command to see all the instances configured and their status is::
gnt-instance list
Do not use the Xen commands to stop instances. If you run for example
xm shutdown or xm destroy on an instance Ganeti will automatically
restart it (via the ``ganeti-watcher``).
Exporting/Importing an instance
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
You can create a snapshot of an instance disk and Ganeti
configuration, which then you can backup, or import into another
cluster. The way to export an instance is::
gnt-backup export -n TARGET_NODE INSTANCE_NAME
The target node can be any node in the cluster with enough space under
``/srv/ganeti`` to hold the instance image. Use the *--noshutdown*
option to snapshot an instance without rebooting it. Any previous
snapshot of the same instance existing cluster-wide under
``/srv/ganeti`` will be removed by this operation: if you want to keep
them move them out of the Ganeti exports directory.
Importing an instance is similar to creating a new one. The command is::
gnt-backup import -n TARGET_NODE -t DISK_TEMPLATE \
--src-node=NODE --src-dir=DIR INSTANCE_NAME
Most of the options available for the command *gnt-instance add* are
supported here too.
High availability features
--------------------------
.. note:: This section only applies to multi-node clusters
Failing over an instance
~~~~~~~~~~~~~~~~~~~~~~~~
If an instance is built in highly available mode you can at any time
fail it over to its secondary node, even if the primary has somehow
failed and it's not up anymore. Doing it is really easy, on the master
node you can just run::
gnt-instance failover INSTANCE_NAME
That's it. After the command completes the secondary node is now the
primary, and vice versa.
Live migrating an instance
~~~~~~~~~~~~~~~~~~~~~~~~~~
If an instance is built in highly available mode, it currently runs
and both its nodes are running fine, you can at migrate it over to its
secondary node, without dowtime. On the master node you need to run::
gnt-instance migrate INSTANCE_NAME
Replacing an instance disks
~~~~~~~~~~~~~~~~~~~~~~~~~~~
So what if instead the secondary node for an instance has failed, or
you plan to remove a node from your cluster, and you failed over all
its instances, but it's still secondary for some? The solution here is
to replace the instance disks, changing the secondary node::
gnt-instance replace-disks -n NODE INSTANCE_NAME
This process is a bit long, but involves no instance downtime, and at
the end of it the instance has changed its secondary node, to which it
can if necessary be failed over.
Failing over the master node
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This is all good as long as the Ganeti Master Node is up. Should it go
down, or should you wish to decommission it, just run on any other
node the command::
gnt-cluster masterfailover
and the node you ran it on is now the new master.
Adding/Removing nodes
~~~~~~~~~~~~~~~~~~~~~
And of course, now that you know how to move instances around, it's
easy to free up a node, and then you can remove it from the cluster::
gnt-node remove NODE_NAME
and maybe add a new one::
gnt-node add --secondary-ip=ADDRESS NODE_NAME
Debugging Features
------------------
At some point you might need to do some debugging operations on your
cluster or on your instances. This section will help you with the most
used debugging functionalities.
Accessing an instance's disks
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
From an instance's primary node you have access to its disks. Never
ever mount the underlying logical volume manually on a fault tolerant
instance, or you risk breaking replication. The correct way to access
them is to run the command::
gnt-instance activate-disks INSTANCE_NAME
And then access the device that gets created. After you've finished
you can deactivate them with the deactivate-disks command, which works
in the same way.
Accessing an instance's console
The command to access a running instance's console is::
gnt-instance console INSTANCE_NAME
Use the console normally and then type ``^]`` when
done, to exit.
Instance OS definitions Debugging
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Should you have any problems with operating systems support the
command to ran to see a complete status for all your nodes is::
gnt-os diagnose
Cluster-wide debugging
~~~~~~~~~~~~~~~~~~~~~~
The *gnt-cluster* command offers several options to run tests or
execute cluster-wide operations. For example::
gnt-cluster command
gnt-cluster copyfile
gnt-cluster verify
gnt-cluster verify-disks
gnt-cluster getmaster
gnt-cluster version
See the man page *gnt-cluster* to know more about their usage.
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