================= Warewulf Overlays ================= So at this point, we have discussed how Warewulf is designed to scalably provision and manage thousands of cluster nodes by utilizing identical stateless boot images. And there-in lies a problem to solve. If these boot images are completely identical, then how do we configure things like hostnames? IP addresses? Or any other node specific custom configurations? While some of this can be managed by services like DHCP, and other bits by configuration management, which can absolutely be done with Warewulf and many people choose to do, these are heavy-weight solutions to a simple problem to solve. Warewulf solves this with overlays and uses overlays in different ways through the provisioning process. A node or profile can configure an overlay in two different ways: * An overlay can be configured to run during boot as part of the ``wwinit`` process. These overlays are called **system overlay** or **wwinit overlays**. * An overlay can be configured to run periodically while the system is running. These overlays are called **runtime overlays** or **generic overlays**. The default profile has both a **wwinit** and a **runtime** overlay configured. Overlays are compiled for each compute node individually. Defined Overlays ================ System or wwinit overlay ------------------------ This overlay contains all the nesscesary scripts to provision a Warewulf node. It is available before the ``systemd`` or other init is called and contains all configurations which are needed to bring up the compute node. It is not updated during run time. Besides the network configurations for * wicked * NetworkManager * EL legacy network scripts it also contains udev rules, which will set the interface name of the first network device to ``eth0``. Before the ``systemd`` init is called, the overlay loops through the scripts in ``/wwinit/warwulf/init.d/*`` which will setup * Ipmi * wwclient * selinux Runtime Overlay or generic Overlay ---------------------------------- The runtime overlay is updated by the ``wwclient`` service on a regular basis (by default, once per minute). In the standard configuration it includes updates for ``/etc/passwd``, ``/etc/group`` and ``/etc/hosts``. Additionally the ``authorized_keys`` file of the root user is updated. It is recommended to use this overlay for dynamic configuration files like ``slurm.conf``. Once the system is provisioned and booted, the ``wwclient`` program (which is provisioned as part of the ``wwinit`` system overlay) will continuously update the node with updates in the runtime overlay. Host Overlay ------------ 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`` Combining Overlays ================== When changing the overlays, it is recommended not to change them, but to add the changed files to a new overlay and combine them in the configuration. This is possible as the configuration fields for the **wwinit** and **runtime** overlays are lists and can contain several overlays. As an example for this, we will overwrite the ``/etc/issue`` file from the **wwinit** overlay. For this we will create a new overlay called welcome and import the file ``/etc/issue`` from the host to it. This overlay is then combined with the existing **wwinit** overlay. .. code-block:: console # wwctl overlay create welcome # wwctl overlay mkdir welcome /etc # wwctl overlay import welcome /etc/issue # wwctl profile set default --wwinit=wwinit,welcome ? Are you sure you want to modify 1 profile(s)? [y/N] y # wwctl profile list default -a |grep welcome default SystemOverlay wwinit,welcome Templates ========= Templates allow you to create dynamic content such that the files downloaded for each node will be customized for that node. Templates allow you to insert everything from variables, to including files from the control node, as well as conditional content and loops. Warewulf uses the ``text/template`` engine to facilitate implementing dynamic content in a simple and standardized manner. All template files will end with the suffix of ``.ww``. That tells Warewulf that when building a file, that it should parse that file as a template. When it does that, the resulting file is static and can have node customizations that are obtained from the node configuration attributes. .. note:: When the file is persisted within the built overlay, the ``.ww`` will be dropped, so ``/etc/hosts.ww`` will end up being ``/etc/hosts``. Using Overlays ============== Warewulf includes a command group for manipulating overlays (``wwctl overlay``). With this you can add, edit, remove, change ownership, permissions, etc. .. note:: There is no possibility to delete files with an overlay! Build ----- .. code-block:: console wwctl overlay build [-H,--hosts|-N,--nodes|-o,--output directory|-O,--overlay-name] nodepattern Without any arguments the command will interpret the templates for all overlays for every compute node and also all the templates in the host overlay. For every overlay of the compute nodes a gzip compressed cpio archive is created. The range of the nodes can be restricted as the last argument. With the ``-H`` flag only the host overlay is built. With the ``-N`` flag only compute node overlays are built. Specific overlays can be selected with ``-O`` flag. For debugging purposes the templates can be written to a directory given via the ``-o`` flag. By default Warewulf will build/update and cache overlays as needed (configurable in the ``warewulf.conf``). Chmod ----- .. code-block:: console wwctl overlay chmod overlay-name filename mode This subcommand changes the permissions of a single file within an overlay. You can use any mode format supported by the chmod command. Chown ----- .. code-block:: console wwctl overlay chown overlay-name filename UID [GID] With this command you can change the ownership of a file within a given overlay to the user specified by UID. Optionally, it will also change group ownership to GID. Create ------ .. code-block:: console wwctl overlay create overlay-name This command creates a new empty overlay with the given name. Delete ------ .. code-block:: console wwctl overlay delete [-f,--force] overlay-name [File [File ...]] Either the given overlay is deleted (must be empty or use the ``--force`` flag) or the specified file within the overlay is deleted. With the ``--parents`` flag the directory of the deleted file is also removed if no other file is in the directory. Edit ---- .. code-block:: console wwctl overlay edit [--mode,-m MODE|--parents,-p] overlay-name file Use this command to edit an existing or a new file in the given overlay. If a the new file ends with a ``.ww`` suffix an example template header is added to the file. With the ``--parents`` flag necessary parent directories for a new file are created. Import ------ .. code-block:: console wwctl overlay import [--mode,-m|--noupdate,-n] overlay-name file-name [new-file-name] The given file is imported to the overlay. If no new-file-name is given, the file will be placed in the overlay at the same path as on the host. With the ``--noupdate`` flag you can block the rebuild of the overlays. List ---- .. code-block:: console wwctl overlay list [--all,-a|--long,-l] [overlay-name] With this command all existing overlays and files in them can be listed. Without any option only the overlay names and their number of files are listed. With the ``--all`` switch also the every file is shown. The ``--long`` option will also display the permissions, UID, and GID of each file. Show ---- .. code-block:: console wwctl overlay show [--quiet,-q|--render,-r nodename] overlay-name file 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.