ceph-volume started initially to provide support for using lvm as the underlying system for an OSD. It is included as part of the tool but it is treated like a plugin.

This modularity, allows for other device or device-like technologies to be able to consume and re-use the utilities and workflows provided.

Adding Plugins

As a Python tool, plugins setuptools entry points. For a new plugin to be available, it should have an entry similar to this in its file:

    entry_points = dict(
        ceph_volume_handlers = [
            'my_command = my_package.my_module:MyClass',

The MyClass should be a class that accepts sys.argv as its argument, ceph-volume will pass that in at instantiation and call them main method.

This is how a plugin for ZFS could look like for example:

class ZFS(object):

    help_menu = 'Deploy OSDs with ZFS'
    _help = """
Use ZFS as the underlying technology for OSDs

--verbose   Increase the verbosity level

    def __init__(self, argv):
        self.argv = argv

    def main(self):
        parser = argparse.ArgumentParser()
        args = parser.parse_args(self.argv)

And its entry point (via setuptools) in would looke like:

entry_points = {
    'ceph_volume_handlers': [
        'zfs = ceph_volume_zfs.zfs:ZFS',

After installation, the zfs subcommand would be listed and could be used as:

ceph-volume zfs