ganeti-os-interface.rst

ganeti-os-interface(7) Ganeti | Version @GANETI_VERSION@

Name

ganeti-os-interface - Specifications for guest OS types

DESCRIPTION

The method of supporting guest operating systems in Ganeti is to have, for each guest OS type, a directory containing a number of required files.

REFERENCE

There are six required files: create, import, export, rename (executables), ganeti_api_version and variants.list (text files).

Common environment

All commands will get their input via environment variables. A common set of variables will be exported for all commands, and some of them might have extra ones. Note that all counts are zero-based.

OS_API_VERSION

The OS API version that the rest of the environment conforms to.

INSTANCE_NAME

The instance name the script should operate on.

INSTANCE_OS, OS_NAME

Both names point to the name of the instance's OS as Ganeti knows it. This can simplify the OS scripts by providing the same scripts under multiple names, and then the scripts can use this name to alter their behaviour.

With OS API 15 changing the script behavior based on this variable is deprecated: OS_VARIANT should be used instead (see below).

OS_VARIANT

The variant of the OS which should be installed. Each OS must support all variants listed under its variants.list file, and may support more. Any more supported variants should be properly documented in the per-OS documentation.

HYPERVISOR

The hypervisor of this instance.

DISK_COUNT

The number of disks the instance has. The actual disk defitions are in a set of additional variables. The instance's disk will be numbered from 0 to this value minus one.

DISK_%N_PATH

The path to the storage for disk N of the instance. This might be either a block device or a regular file, in which case the OS scripts should use losetup (if they need to mount it). E.g. the first disk of the instance might be exported as DISK_0_PATH=/dev/drbd0.

DISK_%N_ACCESS

This is how the hypervisor will export the instance disks: either read-write (rw) or read-only (ro).

DISK_%N_FRONTEND_TYPE

(Optional) If applicable to the current hypervisor type: the type of the device exported by the hypervisor. For example, the Xen HVM hypervisor can export disks as either paravirtual or ioemu.

DISK_%N_BACKEND_TYPE

How files are visible on the node side. This can be either block (when using block devices) or file:type, where type is either loop or blktap depending on how the hypervisor will be configured. Note that not all backend types apply to all hypervisors.

NIC_COUNT

Similar to the DISK_COUNT, this represents the number of NICs of the instance.

NIC_%N_MAC

The MAC address associated with this interface.

NIC_%N_IP

The IP address, if any, associated with the N-th NIC of the instance.

NIC_%N_MODE

The NIC mode, either routed or bridged

NIC_%N_BRIDGE

The bridge to which this NIC will be attached. This variable is defined only when the NIC is in bridged mode.

NIC_%N_LINK

If the NIC is in bridged mode, this is the same as NIC_%N_BRIDGE. If it is in routed mode, the routing table which will be used by the hypervisor to insert the appropriate routes.

NIC_%N_FRONTEND_TYPE

(Optional) If applicable, the type of the exported NIC to the instance, this can be one of: rtl8139, ne2k_pci, ne2k_isa, paravirtual.

DEBUG_LEVEL

If non-zero, this should cause the OS script to generate verbose logs of its execution, for troubleshooting purposes. Currently only 0 and 1 are valid values.

create

The create command is used for creating a new instance from scratch. It has no additional environment variables bside the common ones.

The INSTANCE_NAME variable denotes the name of the instance, which is guaranteed to resolve to an IP address. The create script should configure the instance according to this name. It can configure the IP statically or not, depending on the deployment environment.

The INSTANCE_REINSTALL variable is set to 1 when this create request is reinstalling and existing instance, rather than creating one anew. This can be used, for example, to preserve some data in the old instance in an OS-specific way.

export

This command is used in order to make a backup of a given disk of the instance. The command should write to stdout a dump of the given block device. The output of this program will be passed during restore to the import command.

The specific disk to backup is denoted by two additional environment variables: EXPORT_INDEX which denotes the index in the instance disks structure (and could be used for example to skip the second disk if not needed for backup) and EXPORT_PATH which has the same value as DISK_N_PATH but is duplicate here for easier usage by shell scripts (rather than parse the DISK_... variables).

To provide the user with an estimate on how long the export will take, a predicted size can be written to the file descriptor passed in the variable EXP_SIZE_FD. The value is in bytes and must be terminated by a newline character (\n). Older versions of Ganeti don't support this feature, hence the variable should be checked before use. Example:

if test -n "$EXP_SIZE_FD"; then
  blockdev --getsize64 $blockdev >&$EXP_SIZE_FD
fi

import

The import command is used for restoring an instance from a backup as done by export. The arguments are the similar to those passed to export, whose output will be provided on stdin.

The difference in variables is that the current disk is called by IMPORT_DEVICE and IMPORT_INDEX (instead of EXPORT_...).

rename

This command is used in order to perform a rename at the instance OS level, after the instance has been renamed in Ganeti. The command should do whatever steps are required to ensure that the instance is updated to use the new name, if the operating system supports it.

Note that it is acceptable for the rename script to do nothing at all, however be warned that in this case, there will be a desynchronization between what gnt-instance list shows you and the actual hostname of the instance.

The script will be passed one additional environment variable called OLD_INSTANCE_NAME which holds the old instance name. The INSTANCE_NAME variable holds the new instance name.

A very simple rename script should at least change the hostname and IP address of the instance, leaving the administrator to update the other services.

ganeti_api_version

The ganeti_api_version file is a plain text file containing the version(s) of the guest OS API that this OS definition complies with, one per line. The version documented by this man page is 15, so this file must contain the number 15 followed by a newline if only this version is supported. A script compatible with more than one Ganeti version should contain the most recent version first (i.e. 15), followed by the old version(s) (in this case 10 and/or 5).

variants.list

variants.list is a plain text file containing all the declared supported variants for this OS, one per line. At least one variant must be supported.

NOTES

Backwards compatibility

Ganeti 2.2 is compatible with both API version 10, and 15. In API version 10 the variants.list file is ignored and no OS_VARIANT environment variable is passed.

Common behaviour

All the scripts should display an usage message when called with a wrong number of arguments or when the first argument is -h or --help.

Upgrading from old versions

Version 10 to 15

The variants.list file has been added, so OSes should support at least one variant, declaring it in that file and must be prepared to parse the OS_VARIANT environment variable. OSes are free to support more variants than just the declared ones.

Version 5 to 10

The method for passing data has changed from command line options to environment variables, so scripts should be modified to use these. For an example of how this can be done in a way compatible with both versions, feel free to look at the debootstrap instance's common.sh auxiliary script.

Also, instances can have now a variable number of disks, not only two, and a variable number of NICs (instead of fixed one), so the scripts should deal with this. The biggest change is in the import/export, which are called once per disk, instead of once per instance.

Version 4 to 5

The rename script has been added. If you don't want to do any changes on the instances after a rename, you can migrate the OS definition to version 5 by creating the rename script simply as:

#!/bin/sh

exit 0

Note that the script must be executable.