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Nikos Skalkotos, 09/18/2012 12:21 pm
snf-image¶
Introduction - Features¶
snf-image is a Ganeti OS Definition, primarily used by Synnefo .
It is rewritten from scratch and allows Ganeti to launch instances from predefined or untrusted custom Images. The whole process of deploying an Image onto the block device, as provided by Ganeti, is done in complete isolation from the physical host, enhancing robustness and security (currently supports only KVM based ganeti clusters).
There are also additional hooks that can be enabled at image deployment. They allow for:
- changing the password of root or arbitrary users
- injecting files at arbitrary locations inside the filesystem, e.g., SSH keys
- setting a custom hostname
- re-creating SSH host keys to ensure the image uses unique keys
snf-image has been used successfully to deploy many major Linux distributions (Debian, Ubuntu/Kubuntu, CentOS, Fedora), as well as Windows 2008 R2.
The snf-image Ganeti OS Definition is released under GNU Generic Public Lisence version 2.
Ganeti OS Interface¶
snf-image requires ganeti-os-interface v20 to operate.
It introduces the following OS parameters:
img_id
(required ifconfig_url
is missing): the URI used to identify the image (see here)img_format
(required ifconfig_url
is missing): the image format type (see here)img_passwd
(required ifconfig_url
is missing): the passwd to be injected inside the imageimg_properties
(optional): additional image properties used to customize the image (details)img_personality
(optional): files to be injected into the image filesystem (details).config_url
(optional): the url to download configuration data from
Architecture¶
snf-image is split in two components: A part running on the Ganeti host, with full root privilege (snf-image-host
), and a part running inside an unprivileged, helper VM (snf-image-helper
).
snf-image-host¶
This part implements the Ganeti OS interface. It extracts the Image onto the Ganeti-provided block device, using streaming block I/O (dd
with oflag=direct
), then passes control to snf-image-helper
running inside a helper VM. The helper VM is created using KVM, runs as an unprivileged user, nobody
by default.
There is no restriction on the distribution running inside the helper VM, as long as it executes the snf-image-helper
component automatically upon bootup. The snf-image-update-helper
script is provided with snf-image-host
to automate the creation of a helper VM image based on Debian Stable, using debootstrap
.
The snf-image-helper
component is spawned inside a specific hardware environment:
- The VM features a virtual floppy, containing an
ext2
filesystem with all parameters needed for image customization. - The hard disk of the VM being deployed is accessible as the first
virtio
hard disk. - All kernel/console output is redirected to the first virtual serial console, and eventually finds its way into the OS definition log files that Ganeti maintains.
- The helper VM is expected to output "SUCCESS" to its second serial port if image customization was successful inside the VM.
In any other case, execution of the helper VM orsnf-image-helper
has failed. - The helper VM is expected to shutdown automatically once it is done. Its execution is time-limited; if it has not terminated after a number of seconds, configurable via
/etc/default/snf-image
, it is sent aSIGTERM
and/or aSIGKILL
.
KVM is currently a dependency for snf-image
, meaning it is needed to spawn the helper VM. There is no restriction on the hypervisor used for the actual Ganeti instances. This is not a strict requirement; KVM could be replaced by qemu
, doing full CPU virtualization without any kernel support for spawning the helper VM.
snf-image-helper¶
This part runs inside the helper VM and undertakes customization of the VM being deployed using a number of hooks, or tasks. The tasks run in an environment, specified by rules found in a virtual floppy, placed there by the snf-image-host
component. snf-image-helper
uses runparts
to run tasks found under /usr/lib/snf-image-helper/tasks
by default.
The architecture is presented below:
Graphical Representation¶
Image Names¶
snf-image assumes all image files have the following format:
<image_id>.<image_format>
In order to create an instance with ganeti using an image with filename debian_base-6.0-5-x86_64.extdump
, you need to specify the following OS parameters:
img_format=extdump img_id=debian_base-6.0-5-x86_64
Download¶
Packages¶
Download the latest debian packages (v0.6):Previous versions and source tarballs can be found here:
https://code.grnet.gr/projects/snf-image/files
You can also download the packages from our apt
repo:
Sample Images¶
While developing snf-image, we created and tested a number of images. The following images are basic installations of some popular Linux distributions, that have been tested with snf-image and provided here for testing purposes:
- Debian Squeeze Base System [diskdump] [md5sum] [metadata]
- Debian Desktop [diskdump] [md5sum] [metadata]
- CentOS 6.0 [diskdump] [md5sum] [metadata]
- Fedora Desktop 17 [diskdump] [md5sum] [metadata]
- Ubuntu Desktop 12.04 [diskdump] [md5sum] [metadata]
- Kubuntu Desktop 12.04 [diskdump] [md5sum] [metadata]
After getting familiar with snf-image you can build your own Images (more...), or build upon the ones listed above.
Installation¶
Before installing snf-image be sure to have a working Ganeti installation in your cluster. The installation process should take place in all ganeti nodes. Here we will describe the installation in a single node. The process is identical for all nodes and should be repeated manually or automatically, e.g., with puppet.
- Download the snf-image-host debian package as described in the download section.
- Install the snf-image-host debian package:
# dpkg -i snf-image-host_version.deb
- If the dependencies are not met, install all the dependencies using
apt-get install
(or installsnf-image-host
withapt-get
). - Download the snf-image-helper debian package as described in the download section and store it in a handy location.
- Do NOT install the snf-image-helper debian package in the Ganeti node (the
deb
file should be present in all nodes, but NOT installed in any node). - Configure the package, as described in the next section, before you can start using the new OS Definition.
Configuration¶
In this section, we assume that the image file you want to deploy resides under a local directory.Once you have installed snf-image-host in the Ganeti node, you may need to overwrite the value of some of the following variables in
/etc/default/snf-image
:
- IMAGE_DIR: This should point to the location where the image files are stored [default:
/var/lib/snf-image
]. - HELPER_DIR: This should point to a directory which will host all helper VM files [default:
/var/lib/snf-image/helper
]. This directory should be able to host 700MB. - HELPER_PKG: This should point to the snf-image-helper debian package [default:
/var/lib/snf-image/helper/snf-image-helper_version.deb
].
After all variables are properly set, execute snf-image-update-helper
command to populate HELPER_DIR
with the needed files:
$ /usr/bin/snf-image-update-helper
The above will create the helper VM, install the snf-image-helper package inside it and store all the above under
HELPER_DIR
. If no errors are displayed, you are ready to use the snf-image OS Definition.
Sample Usage¶
diskdump
images¶
If you want to deploy an image of type diskdump
, you need to provide the corresponding img_properties
as described in the Image Format section. If using a diskdump found in the Sample Images list, use the img_properties
described in the image's metadata file. For example:
gnt-instance add -o snf-image+default --os-parameters img_passwd=SamplePassw0rd,img_format=diskdump,img_id=debian_base-6.0-7-x86_64,img_properties='{"OSFAMILY":"linux"\,"ROOT_PARTITION":"1"}' -t plain --disk=0:size=10G --no-name-check --no-ip-check --no-nics test1
extdump
/ntfsdump
images¶
To create a ganeti instance with snf-image using debian_base-6.0-5-x86_64.extdump
hosted under IMAGE_DIR
, use a command like the one below:
gnt-instance add -o snf-image+default --os-parameters img_passwd=SamplePassw0rd,img_format=extdump,img_id=debian_base-6.0-5-x86_64 -t plain --disk=0:size=10G --no-name-check --no-ip-check --no-nics test1
Advanced Usage¶
If you want to learn more and use the advanced features of snf-image please refer to following sections:
1. Supported Image formats
2. Supported Image store locations
3. Progress Monitor Interface
Developers¶
If you are a developer or want to use the latest source code you can download the latest development version by cloning the snf-image git repository:
$ git clone https://code.grnet.gr/git/snf-image
The master branch contains the latest development version
The debian branch contains the master plus the debian packaging directories.
For more information on how to configure, install or package from source, see the Developer's page.
Community & Support¶
Your help is very important. Any contributions and bug reports will be highly appreciated. You can contact the team at:
- Bug reports - feedback - support: synnefo@lists.grnet.gr