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warewulf/userdocs/overlays/overlays.rst
Jonathon Anderson 4005afac4c Add a new OpenAPI v3 REST API to warewulfd at /api 
Co-authored-by: jason yang <jasonyangshadow@gmail.com>

Signed-off-by: Jonathon Anderson <janderson@ciq.com>
2025-04-03 07:12:03 -06:00

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========
Overlays
========
Warewulf supplements provisioned node images with an "overlay" system. Overlays
are collections of files and :ref:`templates` that are rendered
and built per-node and then applied over the image during the provisioning
process.
Overlays are the primary mechanism for adding functionality Warewulf. Much of
even core functionality in Warewulf is implemented as distribution overlays, and
this flexibility is also available for local, custom overlays. By combining
templates with tags, network tags, and resources, the node registry
(``nodes.conf``) can become an expressive metadata store for arbitrary cluster
node configuration.
You can list the available overlays with ``wwctl overlay list``, and the files
within the overlays with ``wwctl overlay list --all``.
.. code-block:: console
# wwctl overlay list --all fstab
OVERLAY NAME FILES/DIRS SITE
------------ ---------- ----
fstab etc/ false
fstab etc/fstab.ww false
Structure
=========
An overlay is a directory that is applied to the root of a cluster node's
runtime file system. The overlay source directory should contain a single
``rootfs`` directory which represents the actual root directory for the overlay.
.. code-block:: none
/usr/share/warewulf/overlays/issue
└── rootfs
└── etc
└── issue.ww
Adding Overlays to Nodes
========================
A node or profile can configure an overlay in two different ways:
* An overlay can be configured to apply only during boot, along with the node
image. These overlays are called **system overlays**.
* An overlay can be configured to also apply periodically while the system is
running. These overlays are called **runtime overlays**.
.. code-block:: shell
wwctl profile set default \
--system-overlays="wwinit,wwclient,fstab,hostname,ssh.host_keys,systemd.netname,NetworkManager" \
--runime-overlays="hosts,ssh.authorized_keys"
Multiple overlays can be applied to a single node, and overlays from multiple
profiles are appended together when applied to a single node.
Building Overlays
=================
Overlays are built (e.g., with ``wwctl overly build``) into compressed overlay
images for distribution to cluster nodes. These images typically match these two
use cases: system and runtime. As such, each cluster node typically has two
overlay images.
.. code-block:: console
# wwctl overlay build
Building system overlay image for n1
Created image for n1 system overlay: /var/lib/warewulf/provision/overlays/n1/__SYSTEM__.img
Compressed image for n1 system overlay: /var/lib/warewulf/provision/overlays/n1/__SYSTEM__.img.gz
Building runtime overlay image for n1
Created image for n1 runtime overlay: /var/lib/warewulf/provision/overlays/n1/__RUNTIME__.img
Compressed image for n1 runtime overlay: /var/lib/warewulf/provision/overlays/n1/__RUNTIME__.img.gz
Overlay images for multiple node are built in parallel. By default, each CPU in
the Warewulf server will build overlays independently. The number of workers can
be specified with the ``--workers`` option.
Warewulf will attempt to build/update overlays as needed (configurable in the
``warewulf.conf``); but not all cases are detected, and manual overlay builds
are often necessary.
Creating and Modifying Overlays
===============================
You can add a new overlay to Warewulf with ``wwctl overlay create``.
.. code-block:: shell
wwctl overlay create issue
A new overlay is just an empty directory. For it to be useful it needs to
contain some files.
For example, ``wwctl overlay import`` imports files from the Warewulf server
into the overlay.
.. code-block:: shell
wwctl overlay import --parents issue /etc/issue
This imports ``/etc/issue`` from the Warewulf server into the new ``issue``
overlay.
.. note::
The ``issue`` overlay already existed as a distribution overlay. Creating one
shadows the distribution overlay with a new site overlay, allowing for local
modification.
Any modification to a distribution overlay first transparently creates a new
site overlay and applies any changes there: distribution overlays should
always remain unmodified.
You can also edit a new or existing overlay file in an interactive editor.
.. code-block:: shell
wwctl overlay edit issue /etc/issue
Use ``wwctl overlay show`` to inspect the content of an overlay file.
.. code-block:: shell
wwctl overlay show issue /etc/issue
Overlay files that end with ``.ww`` are templates. You can use ``wwctl overlay
show --render=<node>`` to show how a given template file would be rendered for
distribution to a given cluster node.
.. code-block:: shell
wwctl overlay delete issue /etc/issue
wwctl overlay import issue /etc/issue /etc/issue.ww
wwctl overlay show issue /etc/issue.ww --render=n1
More information about templates is available in :ref:`its own section
<templates>`.
The content of the file for the given overlay is displayed with this command.
With the ``--render`` option a template is rendered as it will be rendered for
the given node. The node name is a mandatory argument to the ``--render`` flag.
Additional information for the file can be suppressed with the ``--quiet``
option.
.. note::
It is not possible to delete files with an overlay.
Permissions
-----------
Overlay files are distributed to cluster nodes with the same user, group, and
mode that they have on the Warewulf server. Use ``wwctl overlay chown`` and
``wwctl overlay chmod`` to adjust them as necessary.
.. code-block:: shell
wwctl overlay chown issue /etc/issue.ww root root
wwctl overlay chmod issue /etc/issue.ww 0644
Distribution Overlays
=====================
Warewulf distinguishes between **distribution** overlays, which are included
with Warewulf, and **site** overlays, which are created or added locally. A site
overlay always takes precedence over a distribution overlay with the same name.
Any modification of a distribution overlay with ``wwctl`` actually makes changes
to an automatically-generated **site** overlay cloned from the distribution
overlay.
Site overlays are often stored at ``/var/lib/warewulf/overlays/``. Distribution
overlays are often stored at ``/usr/share/warewulf/overlays/``. But these paths
are dependent on compilation, distribution, packaging, and configuration
settings.
wwinit
------
The **wwinit** overlay performs initial configuration of the Warewulf node. Its
`wwinit` script runs before ``systemd`` or other init is called and contains all
configurations which are needed to boot.
In particular:
- Configure the loopback interface
- Configure the BMC based on the node's configuration
- Update PAM configuration to allow missing shadow entries
- Relabel the file system for SELinux
Other overlays may place additional scripts in ``/warewulf/init.d/`` to affect
node configuration in this pre-boot environment.
wwclient
--------
All configured overlays are provisioned initially along with the node image
itself; but **wwclient** periodically fetches and applies the runtime overlay to
allow configuration of some settings without a reboot.
wwclient will contat the ``ipaddr`` value from ``warewulf.conf`` by default.
This can be overridden by specifying a ``WW_IPADDR`` environment variable, which
can be set via an overlay in ``/etc/default/wwclient``.
Network interfaces
------------------
Warewulf ships with support for many different network interface configuration
systems. All of these are applied by default; but the list may be trimmed to
the desired system.
- ifcfg
- NetworkManager
- debian.interfaces
- wicked
Warewulf also configures both systemd and udev with the intended names of
configured network interfaces, typically based on a known MAC address.
- systemd.netname
- udev.netname
.. _dns:
Several of the network configuration overlays support netdev tags to further
customize the interface:
- **``DNS[0-9]*``:** one or more DNS servers
- **``DNSSEARCH``:** domain search path
- **``MASTER``:** the master for a bond interface
NetworkManager
^^^^^^^^^^^^^^
- **``parent_device``:** the parent device of a vlan interface
- **``vlan_id``:** the vlan id for a vlan interface
- **``downdelay``, ``updelay``, ``miimon``, ``mode``, ``xmit_hash_policy``:**
bond device settings
Basics
------
The **hostname** overlay sets the hostname based on the configured Warewulf
node name.
The **hosts** overlay configures ``/etc/hosts`` to include all Warewulf nodes.
The **issue** overlay configures a standard Warewulf status message for display
during login.
The **resolv** overlay configures ``/etc/resolv.conf`` based on the value of
"DNS" nettags. (In most situations this should be unnecessary, as the network
interface configuration should handle this dynamically.)
fstab
-----
The **fstab** overlay configures ``/etc/fstab`` based on the data provided in the "fstab"
resource. It also creates entries for file systems defined by Ignition.
.. code-block:: yaml
nodeprofiles:
default:
resources:
fstab:
- spec: warewulf:/home
file: /home
vfstype: nfs
- spec: warewulf:/opt
file: /opt
vfstype: nfs
ssh
---
Two SSH overlays configure host keys (one set for all node in the cluster) and
``authorized_keys`` for the root account.
- ssh.authorized_keys
- ssh.host_keys
.. _Syncuser:
syncuser
--------
The **syncuser** overlay updates ``/etc/passwd`` and ``/etc/group`` to include
all users on both the Warewulf server and from the image.
To function properly, ``wwctl image syncuser`` (or the ``--syncuser`` option
during ``import``, ``exec``, ``shell``, or ``build``) must have also been run on
the image to synchronize its user and group IDs with those of the server.
If a ``PasswordlessRoot`` tag is set to "true", the overlay will also insert a
"passwordless" root entry. This can be particularly useful for accessing a
cluster node when its network interface is not properly configured.
.. warning::
``PasswordlessRoot`` is not recommended for production; it should only be
used during debugging, when normal authentication is not functional.
ignition
--------
The **ignition** overlay defines partitions and file systems on local disks.
debug
-----
The **debug** overlay is not intended to be used in configuration, but is
provided as an example. In particular, the provided `tstruct.md.ww` demonstrates
the use of most available template metadata.
.. code-block:: shell
wwctl overlay show --render=<nodename> debug tstruct.md.ww
.. _localtime:
localtime
---------
The **localtime** overlay configures the timezone of a cluster node to match
that of the Warewulf server; alternatively, a different timezone may be
specified with a ``localtime`` tag.
.. code-block:: shell
wwctl profile set default --tagadd="localtime=UTC"
host
----
Configuration files used for the configuration of the Warewulf host /
server are stored in the **host** overlay. Unlike other overlays, it
*must* have the name ``host``. Existing files on the host are copied
to backup files with a ``wwbackup`` suffix at the first
run. (Subsequent use of the host overlay won't overwrite existing
``wwbackup`` files.)
The following services get configuration files via the host overlay:
* ssh keys are created with the scrips ``ssh_setup.sh`` and
``ssh_setup.csh``
* hosts entries are created by manipulating ``/etc/hosts`` with the
template ``hosts.ww``
* nfs kernel server receives its exports from the template
``exports.ww``
* the dhcpd service is configured with ``dhcpd.conf.ww``
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