Commit fc3914e6 authored by Iustin Pop's avatar Iustin Pop
Browse files

Document the selection of instance kernels



A simple doc patch to document how to configure the kernels for the
instances.
Signed-off-by: default avatarIustin Pop <iustin@google.com>
Reviewed-by: default avatarMichael Hanselmann <hansmi@google.com>
parent 7adf7814
......@@ -371,6 +371,64 @@ non-managed configuration that the instance had, the transition should
be seamless for the instance. For more than one disk, just pass another
disk parameter (e.g. ``--disk 1:adopt=...``).
Instance kernel selection
+++++++++++++++++++++++++
The kernel that instances uses to bootup can come either from the node,
or from instances themselves, depending on the setup.
Xen-PVM
~~~~~~~
With Xen PVM, there are three options.
First, you can use a kernel from the node, by setting the hypervisor
parameters as such:
- ``kernel_path`` to a valid file on the node (and appropriately
``initrd_path``)
- ``kernel_args`` optionally set to a valid Linux setting (e.g. ``ro``)
- ``root_path`` to a valid setting (e.g. ``/dev/xvda1``)
- ``bootloader_path`` and ``bootloader_args`` to empty
Alternatively, you can delete the kernel management to instances, and
use either ``pvgrub`` or the deprecated ``pygrub``. For this, you must
install the kernels and initrds in the instance, and create a valid grub
v1 configuration file.
For ``pvgrub`` (new in version 2.4.2), you need to set:
- ``kernel_path`` to point to the ``pvgrub`` loader present on the node
(e.g. ``/usr/lib/xen/boot/pv-grub-x86_32.gz``)
- ``kernel_args`` to the path to the grub config file, relative to the
instance (e.g. ``(hd0,0)/grub/menu.lst``)
- ``root_path`` **must** be empty
- ``bootloader_path`` and ``bootloader_args`` to empty
While ``pygrub`` is deprecated, here is how you can configure it:
- ``bootloader_path`` to the pygrub binary (e.g. ``/usr/bin/pygrub``)
- the other settings are not important
More information can be found in the Xen wiki pages for `pvgrub
<http://wiki.xensource.com/xenwiki/PvGrub>`_ and `pygrub
<http://wiki.xensource.com/xenwiki/PyGrub>`_.
KVM
~~~
For KVM also the kernel can be loaded either way.
For loading the kernels from the node, you need to set:
- ``kernel_path`` to a valid value
- ``initrd_path`` optionally set if you use an initrd
- ``kernel_args`` optionally set to a valid value (e.g. ``ro``)
If you want instead to have the instance boot from its disk (and execute
its bootloader), simply set the ``kernel_path`` parameter to an empty
string, and all the others will be ignored.
Instance HA features
--------------------
......
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