warewulf/userdocs/contents/containers.rst

====================
Container Management
====================

Since the inception of Warewulf over 20 years ago, Warewulf has used
the model of the "Virtual Node File System" (VNFS) as a template image
for the compute nodes. This is similar to a golden master image,
except that the node file system exists within a directory on the
Warewulf control node (e.g. a `chroot()`).

In hindsight, we've been using containers all along, but the buzzword
just didn't exist. Over the last 5-6 years, the enterprise has created
a lot of tooling and standards around defining, building,
distributing, securing, and managing containers, so Warewulf (as of
v4.0) now integrates directly within the container ecosystem to
facilitate the process of VNFS image management.

If you are not currently leveraging the container ecosystem in any
other way, you can still build your own chroot directories and use
Warewulf as you always have.

It is important to understand that Warewulf is not running a container
runtime on the nodes. While that is absolutely possible to run
containers from the booted hosts, Warewulf is provisioning the
container image to the bare metal and booting it. This container will
be used as the base operating system and by default it will run
stateless in memory. This means when you reboot the node, the node
persists no information about Warewulf or how it booted.

Container Tools
===============

There are different container managment tools available. Docker is
probably the most recognizable one in the enterprise. Podman is
another one that is gaining traction on the RHEL platforms. In HPC,
Apptainer is the most utilized container management tool. You can use
any of these to create and manage the containers to be later imported
into Warewulf.

Importing From A Registry
=========================

Warewulf supports importing an image from any OCI compliant
registry. This means you can import from a public registry or from a
private registry.

Here is an example of importing from Docker Hub.

.. code-block:: bash

   $ sudo wwctl container import docker://warewulf/rocky rocky-8
   Getting image source signatures
   Copying blob d7f16ed6f451 done
   Copying config da2ca70704 done
   Writing manifest to image destination
   Storing signatures
   [LOG]       info unpack layer: sha256:d7f16ed6f45129c7f4adb3773412def4ba2bf9902de42e86e77379a65d90a984
   Updating the container's /etc/resolv.conf
   Building container: rocky-8

.. note::

    Most containers in Docker Hub are not "bootable", in that, they
    have a limited version of Systemd to make them lighter weight for
    container purposes. For this reason, don't expect any base Docker
    container (e.g. ``docker://rockylinux`` or ``docker://debian``) to
    boot properly. They will not, as they will get stuck into a single
    user mode. The containers in `https://hub.docker.com/u/warewulf
    <https://hub.docker.com/u/warewulf>`_ are not limited and thus
    they boot as you would expect.

Private Registry
----------------

It is possible to use a private registry that is password protected or
does not have the requirement for TLS. In order to do so, you have two
choices for handling the credentials.

* Set environmental variables
* Use ``docker login`` or ``podman login`` which will store the
  credentials locally

Please note, there is no requirement to install and use docker or
podman on your control node just for importing images into Warewulf.

Here are the environmental variables that can be used.

.. code-block:: bash

   WAREWULF_OCI_USERNAME
   WAREWULF_OCI_PASSWORD
   WAREWULF_OCI_NOHTTPS

Here is an example:

.. code-block:: bash

   export WAREWULF_OCI_USERNAME=privateuser
   export WAREWULF_OCI_PASSWORD=super-secret-password-or-token
   sudo -E wwctl import docker://ghcr.io/privatereg/rocky:8

The above is just an example. Consideration should be done before
doing it this way if you are in a security sensitive environment or
shared environments. You would not want these showing up in bash
history or logs.

Syncuser
--------

At import time Warewulf checks if the names of the users on the host
match the users and UIDs/GIDs in the imported container. If there is
mismatch, the import command will print out a warning.  By setting the
``--syncuser`` flag you advise Warewulf to try to syncronize the users
from the host to the container, which means that ``/etc/passwd`` and
``/etc/group`` of the imported container are updated and all the files
belonning to these UIDs and GIDs will also be updated.

A check if the users of the host and container matches can be
triggered with the ``syncuser`` command.

.. code-block:: bash

   wwctl container syncuser container-name

With the ``--write`` flag it will update the container to match the
user database of the host as described above.

.. code-block:: bash

   wwctl container syncuser --write container-name

Listing All Imported Containers
===============================

Once the container has been imported, you can list them all with the
following command:

.. code-block:: bash

   $ sudo wwctl container list
   CONTAINER NAME                      BUILT  NODES
   rocky-8                             true   0

Once a container has been imported and showing up in this list you can
configure it to boot compute nodes.

Making Changes To Containers
============================

Warewulf has a minimal container runtime built into it. This means you
can run commands inside of any of the containers and make changes to
them as follows:

.. code-block:: bash

   $ sudo wwctl container exec rocky-8 /bin/sh
   [rocky-8] Warewulf> cat /etc/rocky-release
   Rocky Linux release 8.4 (Green Obsidian)
   [rocky-8] Warewulf> exit
   Rebuilding container...
   [INFO]     Skipping (VNFS is current)

You can also ``--bind`` directories from your host into the container
when using the exec command. This works as follows:

.. code-block:: bash

   $ sudo wwctl container exec --bind /tmp:/mnt rocky-8 /bin/sh
   [rocky-8] Warewulf>

.. note::

   As with any mount command, both the source and the target must
   exist. This is why the example uses the ``/mnt/`` directory
   location, as it is almost always present and empty in every Linux
   distribution (as prescribed by the LSB file hierarchy standard).

When the command completes, if anything within the container changed,
the container will be rebuilt into a bootable static object
automatically.

If the files ``/etc/passwd`` or ``/etc/group`` were updated, there
will be an additional check to confirm if the users are in sync as
described in `Syncuser`_ section.

Creating Containers From Scratch
================================

You can also create containers from scratch and import those
containers into Warewulf as previous versions of Warewulf did.

Building A Container From Your Host
-----------------------------------

RPM based distributions, as well as Debian variants can all bootstrap
mini ``chroot()`` directories which can then be used to bootstrap your
node's container.

For example, on an RPM based Linux distribution with YUM or DNF, you
can do something like the following:

.. code-block:: bash

   $ sudo yum install --installroot /tmp/newroot basesystem bash \
       chkconfig coreutils e2fsprogs ethtool filesystem findutils \
       gawk grep initscripts iproute iputils net-tools nfs-utils pam \
       psmisc rsync sed setup shadow-utils rsyslog tzdata util-linux \
       words zlib tar less gzip which util-linux openssh-clients \
       openssh-server dhclient pciutils vim-minimal shadow-utils \
       strace cronie crontabs cpio wget rocky-release ipmitool yum \
       NetworkManager

You can do something similar with Debian-based distributions:

.. code-block:: bash

   sudo apt-get install debootstrap
   sudo debootstrap stable /tmp/newroot http://ftp.us.debian.org/debian

Once you have created and modified your new ``chroot()``, you can
import it into Warewulf with the following command:

.. code-block:: bash

   sudo wwctl container import /tmp/newroot containername

Building A Container Using Apptainer
--------------------------------------

Apptainer, a container platform for HPC and performance intensive
applications, can also be used to create node containers for
Warewulf. There are several Apptainer container recipes in the
``containers/Apptainer/`` directory and can be found on GitHub at
`https://github.com/hpcng/warewulf/tree/main/containers/Apptainer
<https://github.com/hpcng/warewulf/tree/main/containers/Apptainer>`_.

You can use these as starting points and adding any additional steps
you want in the ``%post`` section of the recipe file. Once you've done
that, installing Apptainer, building a container sandbox and importing
into Warewulf can be done with the following steps:

.. code-block:: bash

   sudo yum install epel-release
   sudo yum install Apptainer
   sudo Apptainer build --sandbox /tmp/newroot /path/to/Apptainer/recipe.def
   sudo wwctl container import /tmp/newroot containername

Building A Container Using Podman
--------------------------------------

You can also build a container using podman via a `Dockerfile`. For
this step the container must be exported to a tar archive, which then
can be imported to Warewulf. The following steps will create an
openSUSE Leap container and import it to Warewulf:

.. code-block:: bash

  $ sudo podman build -f containers/Docker/openSUSE/Containerfile --tag leap-ww
  $ sudo podman save localhost/leap-ww:latest  -o ~/leap-ww.tar
  $ sudo wwctl container import file://root/leap-ww.tar leap-ww