190 lines
6.1 KiB
Text
190 lines
6.1 KiB
Text
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PreOS
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=====
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Description
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-----------
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With cdist you can install and configure new machines. You can use cdist to
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create PreOS, minimal OS which purpose is to boot new machine.
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After PreOS is booted machine is ready for installing desired OS and
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then it is ready for configuration.
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PreOS creation
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--------------
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With cdist you can create PreOS.
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Currently supported PreOS-es include:
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* debian
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* ubuntu.
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PreOS is created using cdist preos command. preos command has subcommands that
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create the desired PreOS.
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For example, to create ubuntu PreOS:
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.. code-block:: sh
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$ cdist preos ubuntu /preos/preos-ubuntu -b -C \
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-k ~/.ssh/id_rsa.pub -p /preos/pxe-ubuntu \
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-t "/usr/bin/curl 192.168.111.5:3000/install/"
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For more info about available options see cdist manual page.
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This will bootstrap (``-b``) ubuntu PreOS in ``/preos/preos-ubuntu`` directory, it
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will be configured (``-C``) using default built-in initial manifest and with
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specified ssh authorized key (``-k``) and with specified trigger command (``-t``).
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After bootstrapping and configuration PXE
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boot directory will be created (``-p``) in ``/preos/pxe-ubuntu``.
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After PreOS is created new machines can be booted using created PXE (after
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proper dhcp, tftp setting).
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Since PreOS is configured with ssh authorized key it can be accessed throguh
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ssh, i.e. it can be further installed and configured with cdist.
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Triggering installation/configuration
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-------------------------------------
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When installing and configuring new machines using cdist's PreOS concept
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cdist also supports triggering for host installation/configuration.
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At management node you start trigger server as:
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.. code-block:: sh
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$ cdist trigger -b -v -i ~/.cdist/manifest/init-for-triggered
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This will start cdist trigger server in verbose mode. It accepts simple
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requests for configuration and for installation:
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* :strong:`/install/.*` for installation
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* :strong:`/config/.*` for configuration.
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When new machine is booted with PreOS then trigger command is executed.
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Machine will connect to cdist trigger server. If the request is, for example,
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for installation then cdist trigger server will start install command for the
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client host using parameters specified at trigger server startup. For the
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above example that means that client will be installed using specified initial
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manifest ``~/.cdist/manifest/init-for-triggered``.
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Implementing new PreOS sub-command
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----------------------------------
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preos command is implemented as a plugin system. This plugin system scans for
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preos subcommands in ``cdist/preos/`` distribution directory and also in
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``~/.cdist/preos/`` directory if it exists.
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preos subcommand is a module or a class that satisfies the following:
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* it has attribute ``_cdist_preos`` set to ``True``
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* it has function/method ``commandline``.
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For a module based preos subcommand ``commandline`` function accepts a module
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object as its first argument and the list of command line
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arguments (``sys.argv[2:]``).
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For a class preos subcommand ``commandline`` method should be staticmethod and
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it accepts a class object as its first argument and the list of command line
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arguments(``sys.argv[2:]``).
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If preos scanning finds a module/class that has ``_cdist_preos`` set
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to ``True`` and it has function/method ``commandline`` then this module/class is
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registered to preos subcommands. The name of the command is set to ``_preos_name``
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attribute if it exists, otherwise it is set to the module/class name, lowercase.
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When registered preos subcommand is specified as preos command then ``commandline``
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will be called with first argument set to module/class object and second argument
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set to ``sys.argv[2:]``.
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Example writing new dummy preos sub-command
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Module based preos:
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^^^^^^^^^^^^^^^^^^^
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#. Create directory ``~/.cdist/preos/`` if it does not exist
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#. Create ``~/.cdist/preos/netbsd.py`` with the following contents:
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.. code-block:: python
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_preos_name = 'netbsd'
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_cdist_preos = True
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def commandline(cls, args):
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print("NetBSD PreOS: {}".format(args))
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When you try to run this new preos you will get:
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.. code-block:: sh
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$ cdist preos -h
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usage: cdist preos [-h] preos
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Create PreOS
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positional arguments:
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preos PreOS to create, one of: {'netbsd', 'debian', 'ubuntu'}
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optional arguments:
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-h, --help show this help message and exit
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$ cdist preos netbsd
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NetBSD PreOS: []
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Class based preos:
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^^^^^^^^^^^^^^^^^^
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#. Create directory ``~/.cdist/preos/`` if it does not exist
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#. Create ``~/.cdist/preos/freebsd.py`` with the following contents:
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.. code-block:: python
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class FreeBSD(object):
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_cdist_preos = True
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@classmethod
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def commandline(cls, args):
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print("FreeBSD dummy preos: {}".format(args))
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When you try to run this new preos you will get:
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.. code-block:: sh
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$ cdist preos -h
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usage: cdist preos [-h] preos
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Create PreOS
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positional arguments:
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preos PreOS to create, one of: {'freebsd', 'debian', 'ubuntu'}
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optional arguments:
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-h, --help show this help message and exit
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$ cdist preos freebsd
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FreeBSD dummy preos: []
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In the ``commandline`` function/method you have all the freedom to actually create
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PreOS.
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Simple tipical use case for using PreOS and trigger
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---------------------------------------------------
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Tipical use case for using PreOS and trigger command include the following steps.
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#. Create PreOS PXE with ssh key and trigger command for installation.
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.. code-block:: sh
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$ cdist preos ubuntu /preos/ubuntu -b -C \
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-k ~/.ssh/id_rsa.pub -p /preos/pxe \
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-t "/usr/bin/curl 192.168.111.5:3000/install/"
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#. Configure dhcp server and tftp server.
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#. On cdist host (192.168.111.5 from above) start trigger command (it will use
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default init manifest for installation).
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.. code-block:: sh
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$ cdist trigger -b -v
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#. After all is set up start new machines (PXE boot).
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#. New machine boots and executes trigger command, i.e. triggers installation.
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#. Cdist trigger server starts installing host that has triggered it.
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#. After cdist install is finished new host is installed.
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