============================================================== Ganeti Instance Import/Export using Open Virtualization Format ============================================================== Background ========== Open Virtualization Format is an open standard for packaging information regarding virtual machines. It is used, among other, by VMWare, VirtualBox and XenServer. OVF allows users to migrate between virtualization software without the need of reconfiguring hardware, network or operating system. Currently, exporting instance in Ganeti results with a configuration file that is readable only for Ganeti. It disallows the users to change the platform they use without loosing all the machine's configuration. Import function in Ganeti is also currently limited to the previously prepared instances. Implementation of OVF support allows users to migrate to Ganeti from other platforms, thus potentially increasing the usage. It also enables virtual machine end-users to create their own machines (e.g. in VirtualBox or SUSE Studio) and then add them to Ganeti cluster, thus providing better personalization. Overview ======== Open Virtualization Format description -------------------------------------- According to the DMTF document introducing the standard: "The Open Virtualization Format (OVF) Specification describes an open, secure, portable, efficient and extensible format for the packaging and distribution of software to be run in virtual machines." OVF supports both single and multiple- configurations of VMs in one package, is host- and virtualization platform-independent and optimized for distribution (e.g. by allowing usage of public key infrastructure and providing tools for management of basic software licensing). There are no limitations regarding disk images used, as long as the description is provided. Any hardware described in a proper format (i.e. CIM - Common Information Model) is accepted, although there is no guarantee that every virtualization software will support all types of hardware. OVF package should contain exactly one file with ``.ovf`` extension, which is an XML file specifying the following (per virtual machine): - virtual disks - network description - list of virtual hardware - operating system, if any Each of the elements in ``.ovf`` file may, if desired, contain a human-readable description to every piece of information given. Additionally, the package may have some disk image files and other additional resources (e.g. ISO images). In order to provide secure means of distribution for OVF packages, the manifest and certificate are provided. Manifest (``.mf`` file) contains checksums for all the files in OVF package, whereas certificate (``.cert`` file) contains X.509 certificate and a checksum of manifest file. Both files are not compulsory, but certificate requires manifest to be present. Supported disk formats ---------------------- Although OVF is claimed to support 'any disk format', what we are interested in is which formats are supported by VM managers that currently use OVF. - VMWare: ``.vmdk`` (which comes in at least 3 different flavours: ``sparse``, ``compressed`` and ``streamOptimized``) - VirtualBox: ``.vdi`` (VirtualBox's format), ``.vmdk``, ``.vhd`` (Microsoft and XenServer); export disk format is always ``.vmdk`` - XenServer: ``.vmdk``, ``.vhd``; export disk format is always ``.vhd`` - Red Hat Enterprise Virtualization: ``.raw`` (raw disk format), ``.cow`` (qemu's ``QCOW2``) - other: AbiCloud, OpenNode Cloud, SUSE Studio, Morfeo Claudia, OpenStack: mostly ``.vmdk`` In our implementation of the OVF we allow a choice between raw, cow and vmdk disk formats for both import and export. Other formats covertable using ``qemu-img`` are allowed in import mode, but not tested. The justification is the following: - Raw format is supported as it is the main format of disk images used in Ganeti, thus it is effortless to provide support for this format - Cow is used in Qemu - Vmdk is most commonly supported in virtualization software, it also has the advantage of producing relatively small disk images, which is extremely important advantage when moving instances. Import and export - the closer look =================================== This section contains an overview of how different parts of Ganeti's export info are included in ``.ovf`` configuration file. It also explains how import is designed to work with incomplete information. Ganeti's backup format vs OVF ----------------------------- .. highlight:: xml The basic structure of Ganeti ``.ovf`` file is the following:: .. note :: Tags with ``gnt:`` prefix are Ganeti-specific and are not a part of OVF standard. .. highlight:: text Whereas Ganeti's export info is of the following form, ``=>`` showing where will the data be in OVF format:: [instance] disk0_dump = filename => File in References disk0_ivname = name => generated automatically disk0_size = size_in_mb => calculated after disk conversion disk_count = number => generated automatically disk_template = disk_type => gnt:DiskTemplate hypervisor = hyp-name => gnt:Name in gnt:Hypervisor name = inst-name => Name in VirtualSystem nic0_ip = ip => gnt:IPAddress in gnt:Network nic0_link = link => gnt:Link in gnt:Network nic0_mac = mac => gnt:MACAddress in gnt:Network or Item in VirtualHardwareSection nic0_mode = mode => gnt:Mode in gnt:Network nic_count = number => generated automatically tags => gnt:Tags [backend] auto_balanced => gnt:AutoBalance memory = mem_in_mb => Item in VirtualHardwareSection vcpus = number => Item in VirtualHardwareSection [export] compression => ignored os => gnt:Name in gnt:OperatingSystem source => ignored timestamp => ignored version => gnt:VersionId or constants.EXPORT_VERSION [os] => gnt:Parameters in gnt:OperatingSystem [hypervisor] => gnt:Parameters in gnt:Hypervisor In case of multiple networks/disks used by an instance, they will all be saved in appropriate sections as specified above for the first network/disk. Import from other virtualization software ----------------------------------------- In case of importing to Ganeti OVF package generated in other software, e.g. VirtualBox, some fields required for Ganeti to properly handle import may be missing. Most often it will happen that such OVF package will lack the ``gnt:GanetiSection``. If this happens you can specify all the missing parameters in the command line. Please refer to `Command Line`_ section. In the :doc:`ovfconverter` we provide examples of options when converting from VirtualBox, VMWare and OpenSuseStudio. Export to other virtualization software --------------------------------------- When exporting to other virtualization software, you may notice that there is a section ``gnt:GanetiSection``, containing Ganeti-specific information. This may on **rare** cases cause trouble in importing your instance. If that is the case please do one of the two: 1. Export from Ganeti to OVF with ``--external`` option - this will cause to skip the non-standard information. 2. Manually remove the gnt:GanetiSection from the ``.ovf`` file. You will also have to recompute sha1 sum (``sha1sum`` command) of the .ovf file and update your ``.mf`` file with new value. .. note:: Manual change option is only recommended when you have exported your instance with ``-format`` option other that ``raw`` or selected ``--compress``. It saves you the time of converting or compressing the disk image. Planned limitations =================== The limitations regarding import of the OVF instances generated outside Ganeti will be (in general) the same, as limitations for Ganeti itself. The desired behavior in case of encountering unsupported element will be to ignore this element's tag without interruption of the import process. Package ------- There are no limitations regarding support for multiple files in package or packing the OVF package into one OVA (Open Virtual Appliance) file. As for certificates and licenses in the package, their support will be under discussion after completion of the basic features implementation. Multiple Virtual Systems ------------------------ At first only singular instances (i.e. VirtualSystem, not VirtualSystemCollection) will be supported. In the future multi-tiered appliances containing whole nodes (or even clusters) are considered an option. Disks ----- As mentioned, Ganeti will allow export in ``raw``, ``cow`` and ``vmdk`` formats. This means i.e. that the appropriate ``ovf:format`` will be provided. As for import, we will support all formats that ``qemu-img`` can convert to ``raw``. At this point this means ``raw``, ``cow``, ``qcow``, ``qcow2``, ``vmdk`` and ``cloop``. We do not plan for now to support ``vdi`` or ``vhd`` unless they become part of qemu-img supported formats. We plan to support compression both for import and export - in gzip format. There is also a possibility to provide virtual disk in chunks of equal size. The latter will not be implemented in the first version, but we do plan to support it eventually. The ``ovf:format`` tag is not used in our case when importing. Instead we use ``qemu-img info``, which provides enough information for our purposes and is better standardized. Please note, that due to security reasons we require the disk image to be in the same directory as the ``.ovf`` description file for both import and export. In order to completely ignore disk-related information in resulting config file, please use ``--disk-template=diskless`` option. Network ------- Ganeti provides support for routed and bridged mode for the networks. Since the standard OVF format does not contain any information regarding used network type, we add our own source of such information in ``gnt:GanetiSection``. In case this additional information is not present, we perform a simple check - if network name specified in ``NetworkSection`` contains words ``bridged`` or ``routed``, we consider this to be the network type. Otherwise option ``auto`` is chosen, in which case the cluster's default value for that field will be used when importing. This provides a safe fallback in case of NAT networks usage, which are commonly used e.g. in VirtualBox. Hardware -------- The supported hardware is limited to virtual CPUs, RAM memory, disks and networks. In particular, no USB support is currently provided, as Ganeti does not support them. Operating Systems ----------------- Support for different operating systems depends solely on their accessibility for Ganeti instances. List of installed OSes can be checked using ``gnt-os list`` command. References ---------- Files listed in ``ovf:References`` section cannot be hyperlinks. Other ----- The instance name (``gnt:VirtualSystem\gnt:Name`` or command line's ``--name`` option ) has to be resolvable in order for successful import using ``gnt-backup import``. _`Command Line` =============== The basic usage of the ovf tool is one of the following:: ovfconverter import filename ovfconverter export --format= filename This will result in a conversion based solely on the content of provided file. In case some information required to make the conversion is missing, an error will occur. If output directory should be different than the standard Ganeti export directory (usually ``/srv/ganeti/export``), option ``--output-dir`` can be used. If name of resulting entity should be different than the one read from the file, use ``--name`` option. Import options -------------- Import options that ``ovfconverter`` supports include options for backend, disks, hypervisor, networks and operating system. If an option is given, it overrides the values provided in the OVF file. Backend ^^^^^^^ ``--backend=option=value`` can be used to set auto balance, number of vcpus and amount of RAM memory. Please note that when you do not provide full set of options, the omitted ones will be set to cluster defaults (``auto``). Disks ^^^^^ ``--disk-template=diskless`` causes the converter to ignore all other disk option - both from .ovf file and the command line. Other disk template options include ``plain``, ``drdb``, ``file``, ``sharedfile`` and ``blockdev``. ``--disk=number:size=value`` causes to create disks instead of converting them from OVF package; numbers should start with ``0`` and be consecutive. Hypervisor ^^^^^^^^^^ ``-H hypervisor_name`` and ``-H hypervisor_name:option=value`` provide options for hypervisor. Network ^^^^^^^ ``--no-nics`` option causes converter to ignore any network information provided. ``--network=number:option=value`` sets network information according to provided data, ignoring the OVF package configuration. Operating System ^^^^^^^^^^^^^^^^ ``--os-type=type`` sets os type accordingly, this option is **required** when importing from OVF instance not created from Ganeti config file. ``--os-parameters`` provides options for chosen operating system. Tags ^^^^ ``--tags=tag1,tag2,tag3`` is a means of providing tags specific for the instance. After the conversion is completed, you may use ``gnt-backup import`` to import the instance into Ganeti. Example:: ovfconverter import file.ovf --disk-template=diskless \ --os-type=lenny-image \ --backend=vcpus=1,memory=512,auto_balance \ -H:xen-pvm \ --net=0:mode=bridged,link=xen-br0 \ --name=xen.i1 [...] gnt-backup import xen.i1 [...] gnt-instance list Export options -------------- Export options include choice of disk formats to convert the disk image (``--format``) and compression of the disk into gzip format (``--compress``). User has also the choice of allowing to skip the Ganeti-specific part of the OVF document (``--external``). By default, exported OVF package will not be contained in the OVA package, but this may be changed by adding ``--ova`` option. Please note that in order to create an OVF package, it is first required that you export your VM using ``gnt-backup export``. Example:: gnt-backup export -n node1.xen xen.i1 [...] ovfconverter export --format=vmdk --ova --external \ --output-dir=~/xen.i1 \ /srv/ganeti/export/xen.i1.node1.xen/config.ini Implementation details ====================== Disk conversion --------------- Disk conversion for both import and export is done using external tool called ``qemu-img``. The same tool is used to determine the type of disk, as well as its virtual size. Import ------ Import functionality is implemented using two classes - OVFReader and OVFImporter. OVFReader class is used to read the contents of the ``.ovf`` file. Every action that requires ``.ovf`` file access is done through that class. It also performs validation of manifest, if one is present. The result of reading some part of file is typically a dictionary or a string, containing options which correspond to the ones in ``config.ini`` file. Only in case of disks, the resulting value is different - it is then a list of disk names. The reason for that is the need for conversion. OVFImporter class performs all the command-line-like tasks, such as unpacking OVA package, removing temporary directory, converting disk file to raw format or saving the configuration file on disk. It also contains a set of functions that read the options provided in the command line. Typical workflow for the import is very simple: - read the ``.ovf`` file into memory - verify manifest - parse each element of the configuration file: name, disk template, hypervisor, operating system, backend parameters, network and disks - check if option for the element can be read from command line options - if yes: parse options from command line - otherwise: read the appropriate portion of ``.ovf`` file - save gathered information in ``config.ini`` file Export ------ Similar to import, export functionality also uses two classes - OVFWriter and OVFExporter. OVFWriter class produces XML output based on the information given. Its sole role is to separate the creation of ``.ovf`` file content. OVFExporter class gathers information from ``config.ini`` file or command line and performs necessary operations like disk conversion, disk compression, manifest creation and OVA package creation. Typical workflow for the export is even simpler, than for the import: - read the ``config.ini`` file into memory - gather information about certain parts of the instance, convert and compress disks if desired - save each of these elements as a fragment of XML tree - save the XML tree as ``.ovf`` file - create manifest file and fill it with appropriate checksums - if ``--ova`` option was chosen, pack the results into ``.ova`` tarfile Work in progress ---------------- - conversion to/from raw disk should be quicker - add graphic card memory to export information (12 MB of memory) - space requirements for conversion + compression + ova are currently enormous - add support for disks in chunks - add support for certificates - investigate why VMWare's ovftool does not work with ovfconverter's compression and ova packaging -- maybe noteworty: if OVA archive does not have a disk (i.e. in OVA package there is only .ovf ad .mf file), then the ovftool works - investigate why new versions of VirtualBox have problems with OVF created by ovfconverter (everything works fine with 3.16 version, but not with 4.0) .. vim: set textwidth=72 : .. 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