Synnefo » snf-ganeti

<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook V4.2//EN" [

]>

  <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.

        <glosslist>

          <glossentry>

            <glossterm>Cluster</glossterm>

            <glossdef>

              <simpara>

                A set of machines (nodes) that cooperate to offer a

                coherent highly available virtualization service.

              </simpara>

            </glossdef>

          </glossentry>

          <glossentry>

            <glossterm>Node</glossterm>

            <glossdef>

              <simpara>

                A physical machine which is member of a cluster.

                Nodes are the basic cluster infrastructure, and are

                not fault tolerant.

              </simpara>

            </glossdef>

          </glossentry>

          <glossentry>

            <glossterm>Master node</glossterm>

            <glossdef>

              <simpara>

                The node which controls the Cluster, from which all

                Ganeti commands must be given.

              </simpara>

            </glossdef>

          </glossentry>

          <glossentry>

            <glossterm>Instance</glossterm>

            <glossdef>

              <simpara>

                A virtual machine which runs on a cluster. It can be a

                fault tolerant highly available entity.

              </simpara>

            </glossdef>

          </glossentry>

          <glossentry>

            <glossterm>Pool</glossterm>

            <glossdef>

              <simpara>

                A pool is a set of clusters sharing the same network.

              </simpara>

            </glossdef>

          </glossentry>

          <glossentry>

            <glossterm>Meta-Cluster</glossterm>

            <glossdef>

              <simpara>

                Anything that concerns more than one cluster.

              </simpara>

            </glossdef>

          </glossentry>

        </glosslist>

      </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

        <emphasis>Ganeti installation tutorial</emphasis> 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:

        <synopsis>gnt-instance add -n <replaceable>TARGET_NODE</replaceable> -o <replaceable>OS_TYPE</replaceable> -t <replaceable>DISK_TEMPLATE</replaceable> <replaceable>INSTANCE_NAME</replaceable></synopsis>

        The instance name must be resolvable (e.g. 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 (<option>-s</option>)</simpara>

        </listitem>

        <listitem>

          <simpara>The swap size (<option>--swap-size</option>)</simpara>

        </listitem>

        <listitem>

          <simpara>The memory size (<option>-m</option>)</simpara>

        </listitem>

        <listitem>

          <simpara>The number of virtual CPUs (<option>-p</option>)</simpara>

        </listitem>

        <listitem>

          <simpara>The instance ip address (<option>-i</option>) (use the value

            <literal>auto</literal> to make Ganeti record the address from

            dns)</simpara>

        </listitem>

        <listitem>

          <simpara>The bridge to connect the instance to (<option>-b</option>),

            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:</para>

      <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>

            <simpara><emphasis role="strong">Note:</emphasis> This is only

              valid for multi-node clusters using drbd 0.7.</simpara>

            <simpara>

              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.

            </simpara>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term>drbd</term>

          <listitem>

            <simpara><emphasis role="strong">Note:</emphasis> This is only

              valid for multi-node clusters using drbd 8.0.</simpara>

            <simpara>

              This is similar to the

              <replaceable>remote_raid1</replaceable> option, but uses

              new features in drbd 8 to simplify the device

              stack. From a user's point of view, this will improve

              the speed of the <command>replace-disks</command>

              command and (in future versions) provide more

              functionality.

            </simpara>

          </listitem>

        </varlistentry>

      </variablelist>

      <para>

        For example if you want to create an highly available instance use the

        remote_raid1 or drbd disk templates:

        <synopsis>gnt-instance add -n <replaceable>TARGET_NODE</replaceable><optional>:<replaceable>SECONDARY_NODE</replaceable></optional> -o <replaceable>OS_TYPE</replaceable> -t remote_raid1 \

  <replaceable>INSTANCE_NAME</replaceable></synopsis>

      <para>

        To know which operating systems your cluster supports you can use

        <synopsis>gnt-os list</synopsis>

      </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:

        <synopsis>gnt-instance remove <replaceable>INSTANCE_NAME</replaceable></synopsis>

      </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:

        <synopsis>gnt-instance startup <replaceable>INSTANCE_NAME</replaceable></synopsis>

        While the command to stop one is:

        <synopsis>gnt-instance shutdown <replaceable>INSTANCE_NAME</replaceable></synopsis>

        The command to see all the instances configured and their status is:

        <synopsis>gnt-instance list</synopsis>

      </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:

        <synopsis>gnt-backup export -n <replaceable>TARGET_NODE</replaceable> <replaceable>INSTANCE_NAME</replaceable></synopsis>

        The target node can be any node in the cluster with enough

        space under <filename class="directory">/srv/ganeti</filename>

        to hold the instance image. Use the

        <option>--noshutdown</option> option to snapshot an instance

        without rebooting it. Any previous snapshot of the same

        instance existing cluster-wide under <filename

        class="directory">/srv/ganeti</filename> 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 similar to creating a new one. The command is:

        <synopsis>gnt-backup import -n <replaceable>TARGET_NODE</replaceable> -t <replaceable>DISK_TEMPLATE</replaceable> --src-node=<replaceable>NODE</replaceable> --src-dir=DIR INSTANCE_NAME</synopsis>

        Most of the options available for the command

        <emphasis>gnt-instance add</emphasis> are supported here too.

      </para>

    </sect2>

  </sect1>

  <sect1>

    <title>High availability features</title>

    <note>

      <simpara>This section only applies to multi-node clusters.</simpara>

    </note>

    <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:

        <synopsis>gnt-instance failover <replaceable>INSTANCE_NAME</replaceable></synopsis>

        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. This is done in two ways, depending on the disk template type. For <literal>remote_raid1</literal>:

        <synopsis>gnt-instance replace-disks <option>-n <replaceable>NEW_SECONDARY</replaceable></option> <replaceable>INSTANCE_NAME</replaceable></synopsis>

        and for <literal>drbd</literal>:

        <synopsis>gnt-instance replace-disks <option>-s</option> <option>-n <replaceable>NEW_SECONDARY</replaceable></option> <replaceable>INSTANCE_NAME</replaceable></synopsis>

        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:

        <synopsis>gnt-cluster masterfailover</synopsis>

        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:

        <synopsis>gnt-node remove <replaceable>NODE_NAME</replaceable></synopsis>

        and maybe add a new one:

        <synopsis>gnt-node add <optional><option>--secondary-ip=<replaceable>ADDRESS</replaceable></option></optional> <replaceable>NODE_NAME</replaceable>

      </synopsis>

      </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, or you risk breaking

        replication. The correct way to access them is to run the

        command:

        <synopsis>gnt-instance activate-disks <replaceable>INSTANCE_NAME</replaceable></synopsis>

        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.

      </para>

    </sect2>

    <sect2>

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

      <para>

        The command to access a running instance's console is:

        <synopsis>gnt-instance console <replaceable>INSTANCE_NAME</replaceable></synopsis>

        Use the console normally and then type

        <userinput>^]</userinput> when done, to exit.

      </para>

    </sect2>

    <sect2>

      <title>Instance OS definitions 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:

        <synopsis>gnt-os diagnose</synopsis>

      </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:

      <screen>

gnt-cluster command

gnt-cluster copyfile

gnt-cluster verify

gnt-cluster getmaster

gnt-cluster version

      </screen>

        See the man page <citerefentry>

        <refentrytitle>gnt-cluster</refentrytitle>

        <manvolnum>8</manvolnum> </citerefentry> to know more about

        their usage.

      </para>

    </sect2>

  </sect1>

  </article>