332 lines
18 KiB
XML
332 lines
18 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<section xmlns="http://docbook.org/ns/docbook" xmlns:xi="http://www.w3.org/2001/XInclude"
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xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0" xml:id="centos-image">
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<title>Example: CentOS image</title>
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<para>This example shows you how to install a CentOS image and focuses mainly on CentOS 6.4.
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Because the CentOS installation process might differ across versions, the installation steps
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might differ if you use a different version of CentOS.</para>
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<procedure>
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<title>Download a CentOS install ISO</title>
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<step>
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<para>Navigate to the <link
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xlink:href="http://www.centos.org/download/mirrors/">CentOS
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mirrors</link> page.</para>
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</step>
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<step>
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<para>Click one of the <literal>HTTP</literal> links in the right-hand column next to
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one of the mirrors.</para>
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</step>
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<step>
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<para>Click the folder link of the CentOS version that you want to use. For example,
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<literal>6.4/</literal>.</para>
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</step>
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<step>
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<para>Click the <literal>isos/</literal> folder link.</para>
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</step>
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<step>
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<para>Click the <literal>x86_64/</literal> folder link for 64-bit images.</para>
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</step>
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<step>
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<para>Click the netinstall ISO image that you want to download. For example,
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<filename>CentOS-6.4-x86_64-netinstall.iso</filename> is a good choice because
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it is a smaller image that downloads missing packages from the Internet during
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installation.</para>
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</step>
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</procedure>
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<simplesect>
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<title>Start the installation process</title>
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<para>Start the installation process using either <command>virt-manager</command> or
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<command>virt-install</command> as described in the previous section. If you use
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<command>virt-install</command>, do not forget to connect your VNC client to the
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virtual machine.</para>
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<para>Assume that:</para>
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<itemizedlist>
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<listitem>
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<para>The name of your virtual machine image is <literal>centos-6.4</literal>;
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you need this name when you use <command>virsh</command> commands to manipulate the
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state of the image.</para>
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</listitem>
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<listitem>
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<para>You saved the netinstall ISO image to the <filename>/data/isos</filename> directory.</para>
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</listitem>
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</itemizedlist>
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<para>If you use <command>virt-install</command>, the commands should look something like
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this:</para>
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<screen><prompt>#</prompt> <userinput>qemu-img create -f qcow2 /tmp/centos-6.4.qcow2 10G</userinput>
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<prompt>#</prompt> <userinput>virt-install --virt-type kvm --name centos-6.4 --ram 1024 \
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--disk /tmp/centos-6.4.qcow2,format=qcow2 \
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--network network=default \
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--graphics vnc,listen=0.0.0.0 --noautoconsole \
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--os-type=linux --os-variant=rhel6 \
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--extra-args="console=tty0 console=ttyS0,115200n8 serial" \
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--location=/data/isos/CentOS-6.4-x86_64-netinstall.iso</userinput></screen>
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</simplesect>
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<simplesect>
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<title>Step through the installation</title>
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<para>At the initial Installer boot menu, choose the <guilabel>Install or upgrade an
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existing system</guilabel> option. Step through the installation prompts. Accept the
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defaults.</para>
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<mediaobject>
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<imageobject role="fo">
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<imagedata fileref="figures/centos-install.png" format="PNG" scale="60"/>
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</imageobject>
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<imageobject role="html">
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<imagedata fileref="figures/centos-install.png" format="PNG"/>
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</imageobject>
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</mediaobject>
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</simplesect>
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<simplesect>
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<title>Configure TCP/IP</title>
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<para>The default TCP/IP settings are fine. In particular, ensure that Enable IPv4 support
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is enabled with DHCP, which is the default.</para>
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<mediaobject>
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<imageobject>
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<imagedata fileref="figures/centos-tcpip.png" format="PNG" contentwidth="6in"/>
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</imageobject>
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</mediaobject>
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</simplesect>
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<simplesect>
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<title>Point the installer to a CentOS web server</title>
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<para>Choose URL as the installation method.</para>
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<mediaobject>
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<imageobject>
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<imagedata fileref="figures/install-method.png" format="PNG" contentwidth="6in"/>
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</imageobject>
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</mediaobject>
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<para>Depending on the version of CentOS, the net installer requires that the user specify
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either a URL or the web site and a CentOS directory that corresponds to one of the
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CentOS mirrors. If the installer asks for a single URL, a valid URL might be
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<literal>http://mirror.umd.edu/centos/6/os/x86_64</literal>.</para>
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<note>
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<para>Consider using other mirrors as an alternative to
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<literal>mirror.umd.edu</literal>.</para>
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</note>
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<mediaobject>
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<imageobject>
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<imagedata fileref="figures/url-setup.png" format="PNG" contentwidth="6in"/>
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</imageobject>
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</mediaobject>
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<para>If the installer asks for web site name and CentOS directory separately, you might
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enter:</para>
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<itemizedlist>
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<listitem>
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<para>Web site name: <literal>mirror.umd.edu</literal></para>
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</listitem>
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<listitem>
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<para>CentOS directory: <literal>centos/6/os/x86_64</literal></para>
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</listitem>
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</itemizedlist>
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<para>See <link xlink:href="http://www.centos.org/download/mirrors/"
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>CentOS mirror page</link> to get a full list of mirrors, click on the "HTTP" link
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of a mirror to retrieve the web site name of a mirror.</para>
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</simplesect>
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<simplesect>
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<title>Storage devices</title>
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<para>If prompted about which type of devices your installation uses, choose <guilabel>Basic
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Storage Devices</guilabel>.</para>
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</simplesect>
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<simplesect>
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<title>Hostname</title>
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<para>The installer may ask you to choose a host name. The default
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(<literal>localhost.localdomain</literal>) is fine. You install the <systemitem
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class="service">cloud-init</systemitem> package later, which sets the host name on
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boot when a new instance is provisioned using this image.</para>
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</simplesect>
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<simplesect>
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<title>Partition the disks</title>
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<para>There are different options for partitioning the disks. The default installation uses
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LVM partitions, and creates three partitions (<filename>/boot</filename>,
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<filename>/</filename>, swap), which works fine. Alternatively, you might want to
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create a single ext4 partition that is mounted to "<literal>/</literal>", which also
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works fine.</para>
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<para>If unsure, use the default partition scheme for the installer because no scheme is
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better than another.</para>
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</simplesect>
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<simplesect>
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<title>Step through the installation</title>
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<para>Step through the installation, using the default options. The simplest thing to do is
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to choose the "Basic Server" install (may be called "Server" install on older versions
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of CentOS), which installs an SSH server.</para>
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</simplesect>
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<simplesect>
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<title>Detach the CD-ROM and reboot</title>
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<para>After the install completes, the <guilabel>Congratulations, your CentOS installation
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is complete</guilabel> screen appears.</para>
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<mediaobject>
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<imageobject>
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<imagedata fileref="figures/centos-complete.png" format="PNG" contentwidth="6in"/>
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</imageobject>
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</mediaobject>
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<para>To eject a disk by using the <command>virsh</command> command, libvirt requires that
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you attach an empty disk at the same target that the CDROM was previously attached,
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which should be <literal>hdc</literal>. You can confirm the appropriate target using the
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<command>dom dumpxml <replaceable>vm-image</replaceable></command> command.</para>
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<screen><prompt>#</prompt> <userinput>virsh dumpxml centos-6.4</userinput>
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<computeroutput><domain type='kvm'>
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<name>centos-6.4</name>
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...
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<disk type='block' device='cdrom'>
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<driver name='qemu' type='raw'/>
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<target dev='hdc' bus='ide'/>
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<readonly/>
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<address type='drive' controller='0' bus='1' target='0' unit='0'/>
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</disk>
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...
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</domain>
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</computeroutput></screen>
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<para>Run the following commands from the host to eject the disk and reboot using virsh, as
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root. If you are using virt-manager, the commands below will work, but you can also use
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the GUI to detach and reboot it by manually stopping and starting.</para>
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<screen><prompt>#</prompt> <userinput>virsh attach-disk --type cdrom --mode readonly centos-6.4 "" hdc</userinput>
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<prompt>#</prompt> <userinput>virsh destroy centos-6.4</userinput>
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<prompt>#</prompt> <userinput>virsh start centos-6.4</userinput></screen>
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</simplesect>
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<simplesect>
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<title>Log in to newly created image</title>
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<para>When you boot for the first time after installation, you might be prompted about
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authentication tools. Select <guilabel>Exit</guilabel>. Then, log in as root.</para>
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</simplesect>
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<simplesect>
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<title>Install the ACPI service</title>
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<para>To enable the hypervisor to reboot or shutdown an instance, you
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must install and run the <systemitem
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class="service">acpid</systemitem> service on the guest
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system.</para>
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<para>Run the following commands inside the CentOS guest to install the
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ACPI service and configure it to start when the system
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boots:</para>
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<screen><prompt>#</prompt> <userinput>yum install acpid</userinput>
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<prompt>#</prompt> <userinput>chkconfig acpid on</userinput></screen>
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</simplesect>
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<simplesect>
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<title>Configure to fetch metadata</title>
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<para>An instance must interact with the metadata service to perform several tasks on start
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up. For example, the instance must get the ssh public key and run the user data script.
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To ensure that the instance performs these tasks, use one of these methods:</para>
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<itemizedlist>
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<listitem>
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<para>Install a <systemitem class="service">cloud-init</systemitem> RPM, which is a
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port of the Ubuntu <link xlink:href="https://launchpad.net/cloud-init"
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>cloud-init</link> package. This is the recommended approach.</para>
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</listitem>
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<listitem>
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<para>Modify <filename>/etc/rc.local</filename> to fetch desired information from
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the metadata service, as described in the next section.</para>
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</listitem>
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</itemizedlist>
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</simplesect>
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<simplesect>
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<title>Use cloud-init to fetch the public key</title>
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<para>The <systemitem class="service">cloud-init</systemitem> package automatically fetches
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the public key from the metadata server and places the key in an account. You can
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install <systemitem class="service">cloud-init</systemitem> inside the CentOS guest by
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adding the EPEL repo:</para>
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<screen><prompt>#</prompt> <userinput>yum install http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm</userinput>
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<prompt>#</prompt> <userinput>yum install cloud-init</userinput></screen>
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<para>The account varies by distribution. On Ubuntu-based virtual machines, the account is
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called <literal>ubuntu</literal>. On Fedora-based virtual machines, the account is
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called <literal>ec2-user</literal>.</para>
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<para>You can change the name of the account used by <systemitem class="service"
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>cloud-init</systemitem> by editing the <filename>/etc/cloud/cloud.cfg</filename>
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file and adding a line with a different user. For example, to configure <systemitem
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class="service">cloud-init</systemitem> to put the key in an account named
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<literal>admin</literal>, add this line to the configuration file:</para>
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<programlisting>user: admin</programlisting>
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</simplesect>
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<simplesect>
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<title>Write a script to fetch the public key (if no cloud-init)</title>
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<para>If you are not able to install the <systemitem class="service">cloud-init</systemitem>
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package in your image, to fetch the ssh public key and add it to the root account, edit
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the <filename>/etc/rc.d/rc.local</filename> file and add the following lines before the line
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<literal>touch /var/lock/subsys/local</literal>:</para>
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<programlisting language="bash">if [ ! -d /root/.ssh ]; then
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mkdir -p /root/.ssh
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chmod 700 /root/.ssh
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fi
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# Fetch public key using HTTP
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ATTEMPTS=30
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FAILED=0
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while [ ! -f /root/.ssh/authorized_keys ]; do
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curl -f http://169.254.169.254/latest/meta-data/public-keys/0/openssh-key \
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> /tmp/metadata-key 2>/dev/null
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if [ \$? -eq 0 ]; then
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cat /tmp/metadata-key >> /root/.ssh/authorized_keys
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chmod 0600 /root/.ssh/authorized_keys
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restorecon /root/.ssh/authorized_keys
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rm -f /tmp/metadata-key
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echo "Successfully retrieved public key from instance metadata"
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echo "*****************"
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echo "AUTHORIZED KEYS"
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echo "*****************"
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cat /root/.ssh/authorized_keys
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echo "*****************"
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done</programlisting>
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<note>
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<para>Some VNC clients replace the colon (<literal>:</literal>) with a semicolon
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(<literal>;</literal>) and the underscore (<literal>_</literal>) with a hyphen
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(<literal>-</literal>). Make sure to specify <literal>http:</literal> and not
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<literal>http;</literal>. Make sure to specify
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<literal>authorized_keys</literal> and not
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<literal>authorized-keys</literal>.</para>
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</note>
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<note>
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<para>The previous script only gets the ssh public key from the metadata server. It does
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not get user data, which is optional data that can be passed by the user when
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requesting a new instance. User data is often used to run a custom script when an
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instance boots.</para>
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<para>As the OpenStack metadata service is compatible with version 2009-04-04 of the
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Amazon EC2 metadata service, consult the Amazon EC2 documentation on <link
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xlink:href="http://docs.amazonwebservices.com/AWSEC2/2009-04-04/UserGuide/AESDG-chapter-instancedata.html"
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>Using Instance Metadata</link> for details on how to get user data.</para>
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</note>
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</simplesect>
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<simplesect>
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<title>Disable the zeroconf route</title>
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<para>For the instance to access the metadata service, you must disable the default zeroconf
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route:</para>
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<screen><prompt>#</prompt> <userinput>echo "NOZEROCONF=yes" >> /etc/sysconfig/network</userinput></screen>
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</simplesect>
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<simplesect>
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<title>Configure console</title>
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<para>For the <command>nova console-log</command> command to work properly on CentOS
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6.<replaceable>x</replaceable>, you might need to add the following lines to the
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<filename>/boot/grub/menu.lst</filename> file:</para>
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<programlisting>serial --unit=0 --speed=115200
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terminal --timeout=10 console serial
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# Edit the kernel line to add the console entries
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kernel <replaceable>...</replaceable> console=tty0 console=ttyS0,115200n8</programlisting>
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</simplesect>
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<simplesect>
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<title>Shut down the instance</title>
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<para>From inside the instance, as root:</para>
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<screen><prompt>#</prompt> <userinput>/sbin/shutdown -h now</userinput></screen>
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</simplesect>
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<simplesect>
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<title>Clean up (remove MAC address details)</title>
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<para>The operating system records the MAC address of the virtual Ethernet card in locations
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such as <filename>/etc/sysconfig/network-scripts/ifcfg-eth0</filename> and
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<filename>/etc/udev/rules.d/70-persistent-net.rules</filename> during the instance
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process. However, each time the image boots up, the virtual Ethernet card will have a
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different MAC address, so this information must be deleted from the configuration
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file.</para>
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<para>There is a utility called <command>virt-sysprep</command>, that performs various
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cleanup tasks such as removing the MAC address references. It will clean up a virtual
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machine image in place:</para>
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<screen><prompt>#</prompt> <userinput>virt-sysprep -d centos-6.4</userinput></screen>
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</simplesect>
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<simplesect>
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<title>Undefine the libvirt domain</title>
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<para>Now that you can upload the image to the Image Service, you no longer need to have
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this virtual machine image managed by libvirt. Use the <command>virsh undefine
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<replaceable>vm-image</replaceable></command> command to inform libvirt:</para>
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<screen><prompt>#</prompt> <userinput>virsh undefine centos-6.4</userinput></screen>
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</simplesect>
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<simplesect>
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<title>Image is complete</title>
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<para>The underlying image file that you created with <command>qemu-img create</command> is
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ready to be uploaded. For example, you can upload the
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<filename>/tmp/centos-6.4.qcow2</filename> image to the Image Service.</para>
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</simplesect>
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</section>
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