[ganeti-local] / docs / admin.sgml

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  <article class="specification">
  <articleinfo>
    <title>Ganeti administrator's guide</title>
  </articleinfo>
  <para>Documents Ganeti version 1.2</para>
  <sect1>
    <title>Introduction</title>

    <para>Ganeti is a virtualization cluster management software. You are
    expected to be a system administrator familiar with your Linux distribution
    and the Xen virtualization environment before using it.
    </para>

    <para>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.
    </para>

    <para>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:
      <itemizedlist>
        <listitem>
          <simpara>Instance Management</simpara>
        </listitem>
        <listitem>
          <simpara>High Availability Features</simpara>
        </listitem>
        <listitem>
          <simpara>Debugging Features</simpara>
        </listitem>
      </itemizedlist>
    </para>

    <sect2>
      <title>Ganeti Terminology</title>

      <para>This section provides a small introduction to Ganeti terminology,
      which might be useful to read the rest of the document.

      <variablelist>
        <varlistentry>
          <term>Cluster</term>
          <listitem><para>A set of machines (nodes) that cooperate to offer a
          coherent highly available virtualization service.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term>Node</term>
          <listitem><para>A physical machine which is member of a cluster.
          Nodes are the basic cluster infrastructure, and are not fault
          tolerant.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term>Master Node</term>
          <listitem><para>The node which controls the Cluster, from which all
          Ganeti commands must be given.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term>Instance</term>
          <listitem><para>A virtual machine which runs on a cluster. It can be
          a fault tolerant highly available entity.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term>Pool</term>
          <listitem><para>A pool is a set of clusters sharing the same
          network.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term>Meta-Cluster</term>
          <listitem><para>Anything that concerns more than one
          cluster.</para></listitem>
        </varlistentry>

      </variablelist>

      </para>
    </sect2>

    <sect2>
      <title>Prerequisites</title>

      <para>You need to have your Ganeti cluster installed and configured
      before you try any of the commands in this document. Please follow the
      "installing tutorial" for instructions on how to do that.
      </para>
    </sect2>

  </sect1>

  <sect1>
    <title>Managing Instances</title>

    <sect2>
      <title>Adding/Removing an instance</title>

      <para>Adding a new virtual instance to your Ganeti cluster is really
      easy. The command is:
      <programlisting>
gnt-instance add -n TARGET_NODE -o OS_TYPE -t DISK_TEMPLATE INSTANCE_NAME
      </programlisting>
      The instance name must exist in dns and of course map to an address in
      the same subnet as the cluster itself. Options you can give to this
      command include:
      <itemizedlist>
        <listitem>
          <simpara>The disk size (-s)</simpara>
        </listitem>
        <listitem>
          <simpara>The swap size (--swap-size)</simpara>
        </listitem>
        <listitem>
          <simpara>The memory size (-m)</simpara>
        </listitem>
        <listitem>
          <simpara>The number of virtual CPUs (-p)</simpara>
        </listitem>
        <listitem>
          <simpara>The instance ip address (-i) (use -i auto to make Ganeti
          record the address from dns)</simpara>
        </listitem>
        <listitem>
          <simpara>The bridge to connect the instance to (-b), if you don't
          want to use the default one</simpara>
        </listitem>
      </itemizedlist>
      </para>

      <para>There are four types of disk template you can choose from:

      <variablelist>
        <varlistentry>
          <term>diskless</term>
          <listitem><para>The instance has no disks. Only used for special
          purpouse operating systems or for testing.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term>plain</term>
          <listitem><para>The instance will use LVM devices as backend for its
          disks. No redundancy is provided.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term>local_raid1</term>
          <listitem><para>A local mirror is set between LVM devices to back the
          instance. This provides some redundancy for the instance's
          data.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term>remote_raid1</term>
          <listitem><para>A mirror is set between the local node and a remote
          one, which must be specified with the --secondary-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.
          </para></listitem>
        </varlistentry>

      </variablelist>

      For example if you want to create an highly available instance use the
      remote_raid1 disk template:
      <programlisting>
gnt-instance add -n TARGET_NODE -o OS_TYPE -t remote_raid1 \
  --secondary-node=SECONDARY_NODE INSTANCE_NAME
      </programlisting>
      To know which operating systems your cluster supports you can use:
      <programlisting>
gnt-os list
      </programlisting>
      </para>

      <para>
      Removing an instance is even easier than creating one. This operation is
      non-reversible and destroys all the contents of your instance. Use with
      care:
      <programlisting>
gnt-instance remove INSTANCE_NAME
      </programlisting>
      </para>
    </sect2>

    <sect2>
      <title>Starting/Stopping an instance</title>

      <para>Instances are automatically started at instance creation time. To
      manually start one which is currently stopped you can run:
      <programlisting>
gnt-instance startup INSTANCE_NAME
      </programlisting>
      While the command to stop one is:
      <programlisting>
gnt-instance shutdown INSTANCE_NAME
      </programlisting>
      The command to see all the instances configured and their status is:
      <programlisting>
gnt-instance list
      </programlisting>
      </para>

      <para>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
      <citerefentry><refentrytitle>ganeti-watcher</refentrytitle>
      <manvolnum>8</manvolnum></citerefentry>)
      </para>

    </sect2>

    <sect2>
      <title>Exporting/Importing an instance</title>

      <para>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:
      <programlisting>
gnt-backup export -n TARGET_NODE INSTANCE_NAME
      </programlisting>
      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.
      </para>

      <para>Importing an instance is as easy as creating a new one. The command
      is:
      <programlisting>
gnt-backup import -n TRGT_NODE -t DISK_TMPL --src-node=NODE --src-dir=DIR INST_NAME
      </programlisting>
      Most of the options available for gnt-instance add are supported here
      too.
      </para>
    </sect2>

  </sect1>


  <sect1>
    <title>High availability features</title>

    <sect2>
      <title>Failing over an instance</title>

      <para>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:
      <programlisting>
gnt-instance failover INSTANCE_NAME
      </programlisting>
      That's it. After the command completes the secondary node is now the
      primary, and vice versa.
      </para>
    </sect2>
    <sect2>
      <title>Replacing an instance disks</title>

      <para>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:
      <programlisting>
gnt-instance replace-disks -n NEW_SECONDARY INSTANCE_NAME
      </programlisting>
      This process is a bit longer, 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.
      </para>
    </sect2>
    <sect2>
      <title>Failing over the master node</title>

      <para>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:
      <programlisting>
gnt-cluster masterfailover
      </programlisting>
      and the node you ran it on is now the new master.
      </para>
    </sect2>
    <sect2>
      <title>Adding/Removing nodes</title>

      <para>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:
      <programlisting>
gnt-node remove NODE_NAME
      </programlisting>
      and maybe add a new one:
      <programlisting>
gnt-node add [--secondary-ip=ADDRESS] NODE_NAME
      </programlisting>
      </para>
    </sect2>
  </sect1>

  <sect1>
    <title>Debugging Features</title>

    <para>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.
    </para>

    <sect2>
      <title>Accessing an instance's disks</title>

      <para>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, though or you risk breaking replication. The correct way to
      access them is to run the command:
      <programlisting>
gnt-instance activate-disks INSTANCE_NAME
      </programlisting>
      And then access the device that gets created.  Of course after you've
      finished you can deactivate them with the deactivate-disks command, which
      works in the same way.
      </para>
    </sect2>

    <sect2>
      <title>Accessing an instance's console</title>

      <para>The command to access a running instance's console is:
      <programlisting>
gnt-instance console INSTANCE_NAME
      </programlisting>
      Use the console normally and then type ^] when done, to exit.
      </para>
    </sect2>

    <sect2>
      <title>Instance Operating System Debugging</title>

      <para>Should you have any problems with operating systems support the
      command to ran to see a complete status for all your nodes is:
      <programlisting>
gnt-os diagnose
      </programlisting>
      </para>

    </sect2>

    <sect2>
      <title>Cluster-wide debugging</title>

      <para>The gnt-cluster command offers several options to run tests or
      execute cluster-wide operations. For example:
      <programlisting>
gnt-cluster command
gnt-cluster copyfile
gnt-cluster verify
gnt-cluster getmaster
gnt-cluster version
      </programlisting>
      See the respective help to know more about their usage.
      </para>
    </sect2>

  </sect1>

  </article>