Wednesday May 16, 2012

More on templates and first boot configuration

A little while back I wrote something up about building appliances (physical/virtual) using Oracle Linux. We build a whole set of Oracle VM templates and release them on our edelivery site. But some of what we use inside these templates can be more generically applied... Let me explain..

A few years ago we created a Linux rpm called oraclevm-template-config. This is a very small package that contains a number of scripts that esssentially do the following:

  • install a service oraclevm-template-config that checks at boot time whether it needs to run or not
  • provides a default first boot configuration service for root password, network setup
  • provides a default cleanup script so that you can re-run this on an existing system, at next boot
  • provides a small set of library calls to use those functions in your own scripts
  • allows you to define your own first boot configuration scripts for your own applications to run
  • regenerates ssh host keys
  • all input was done on the local console or through kernel boot line parameters
  • These things are very straightforward and we wrote it specifically to build Oracle VM templates but there was nothing specific to Oracle VM or virtualization there. The newer version of this, which we released along with Oracle VM 3.x is very much tied into Oracle VM. In the new version (3.x) we integrate the first boot scripts and the configuration scripts with the Oracle VM VM api where it's now possible to send remote VM messages to configure the VM. So in order to automate deployment and have very integrated and fancy assemblies or Oracle VM based templates, this is the way to go. If, however, you want something very simple, with lcoal console (physical or virtual), where it can be on a physical server where you want to reboot and reconfigure and install, whether this is a VirtualBox VM or an Oracle VM VM or, for that matter any other Virtualization technology based VM. the older version is quite usable. I tend to use that one for the VirtualBox templates that I create all the time.

    We just published this rpm on http://public-yum.oracle.com. The rpm can be directly downloaded for Oracle Linux 5, here. Or when you have a system registered with public-yum or with ULN it is also in the add-ons channel. If you have a yum repo config then just enable the addon channel and you can simple type yum install oraclevm-template-config.

    So what are some of the basics you can do :

    initial install By default when you install template config, you have a service that provides the basic, configure root password, setup local network at what's called firstboot. To enable this to happen at the next reboot (which one can then call firstboot), just simple type /usr/sbin/oraclevm-template --enable. There is a simple default cleanup script which un-configures the network and removes ssh keys : /usr/sbin/oraclevm-template --cleanup. Keep in mind that when you run this script, the network will reset to dhcp and you will lose your network connection if you are in a remote ssh session.

    So once you do this and reboot your server or your VM. The next reboot will automatically start /usr/sbin/oraclevm-template --config and go through the questionnaire.

    The base configuration script is /etc/sysconfig/oraclevm-template. If you enable the service, you will see RUN_TEMPLATE_CONFIG=YES. This means next boot it will run. There is also a log file /var/log/oraclevm-template.log.

    If all you need is a simple way of packaging a VM or configure a physical server that deals with network setup, the above is enough. If you have your own software installed and it can handle IP changes without reconfiguration, then you can create an appliance and once firstboot happens, the configuration is set, network is setup, your application comes up and you're done. However, in some cases you want to run your own scripts and integrate with this template configuration. We also handle that case...

    If you write your own shell script (or really any script) that you install on the system, you can add that script to /etc/sysconfig/oraclevm-template and instead of doing the default firstboot run, it will at firstboot (when you call --enable) execute your script instead. Simply by setting TEMPLATE_CONFIG_SCRIPT=/myscript.sh. Inside that script you can do whatever you want... You can also provide a cleanup script for --cleanup, using TEMPLATE_CLEANUPS_SCRIPT=mycleanupscript.sh.

    Keep in mind that we do not automatically run --cleanup, this is a manual step. I would recommend doing the following :

  • /usr/sbin/oraclevm-template --enable
  • /usr/sbin/oraclevm-template --cleanup
  • history -c
  • shutdown -h now
  • We provide a few default function you can include in your own scripts. These functions are defined in /usr/lib/oraclevm-template/functions just source them in your bash script.

    ovm_configure_network [dhcp [hostname]] | [static] | [ip_adddress netmask gateway dns_server hostname]

    You can call this like ovm_configure_network "dhcp" in your script and it will configure your network that way. If you set it to static then there will be a dialog for entering ip, hostname, gateway, netmask, dns, or if you provide that in your function call it will just set the changes without dialog.

    ovm_cleanup_os
    A simple OS cleanup. This resets the network to dhcp and cleans up ssh keys.

    ovm_disable_firewall
    disable iptables

    press_anykey
    Shows user input to enter a key in your script execution flow

    ovm_error_message Displays an error message to the screen and also to /var/log/oraclevm-template.log

    ovm_info_message Displays an informational message to the screen and also to /var/log/oraclevm-template.log

    ovm_warn_message Displays a warning message to the screen and also to /var/log/oraclevm-template.log

    All of the above is very simple, yet very powerful. Like I mentioned in the beginning, I use this all the time when creating both VirtualBox and Oracle VM server templates and it makes my life so much easier. People often write these on their own but I wanted to share how to do this so, when you use Oracle Linux, and/or Oracle VM Server or Oracle VM VirtualBox or anything else, and you're building a cool appliance, physical or virtual, use it and you don't even need a support subscription to download it:)...

    About

    Wim Coekaerts is the Senior Vice President of Linux and Virtualization Engineering for Oracle. He is responsible for Oracle's complete desktop to data center virtualization product line and the Oracle Linux support program.

    You can follow him on Twitter at @wimcoekaerts

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