=============================
 Block Devices and OpenStack
=============================

You may use Ceph block device images with OpenStack through ``libvirt``, which
configures the QEMU interface to ``librbd``. Ceph stripes block device images as
objects across the cluster, which means that large Ceph block device images have
better performance than a standalone server!

To use Ceph block devices with OpenStack, you must install QEMU, ``libvirt``,
and OpenStack first. We recommend using a separate physical host for your
OpenStack installation. OpenStack recommends a minimum of 8GB of RAM and a
quad-core processor. The following diagram depicts the OpenStack/Ceph
technology stack.


.. ditaa::  +---------------------------------------------------+
            |                    OpenStack                      |
            +---------------------------------------------------+
            |                     libvirt                       |
            +------------------------+--------------------------+
                                     |
                                     | configures
                                     v
            +---------------------------------------------------+
            |                       QEMU                        |
            +---------------------------------------------------+
            |                      librbd                       |
            +---------------------------------------------------+
            |                     librados                      |
            +------------------------+-+------------------------+
            |          OSDs          | |        Monitors        |
            +------------------------+ +------------------------+

.. important:: To use Ceph block devices with OpenStack, you must have a running Ceph cluster.

Two parts of OpenStack integrate with Ceph's block devices: 

- **Images**: OpenStack Glance manages images for VMs. Images
  are immutable. OpenStack treats images as binary blobs and
  downloads them accordingly. 

- **Volumes**: Volumes are block devices. OpenStack uses volumes
  to boot VMs, or to attach volumes to running VMs. OpenStack
  manages volumes using ``nova-volume`` prior to the Folsom 
  release. OpenStack manages volumes using Cinder services 
  beginning with the Folsom release.

Beginning with OpenStack Folsom and Ceph 0.52, you can use  OpenStack Glance to
store images in a Ceph block device, and  you can use Cinder or ``nova-volume``
to boot a VM using a copy-on-write clone of an image.

The instructions below detail the setup for Glance and Nova/Cinder, although
they do not have to be used together. You may store images in Ceph block devices
while running VMs using a local disk, or vice versa.

Create a Pool
=============

By default, Ceph block devices use the ``rbd`` pool. You may use any available
pool. We recommend creating a pool for Nova/Cinder and a pool for Glance. Ensure
your Ceph cluster is running, then create the pools. ::

    ceph osd pool create volumes 128
    ceph osd pool create images 128

See `Create a Pool`_ for detail on specifying the number of placement groups for
your pools, and `Placement Groups`_ for details on the number of placement
groups you should set for your pools.

.. _Create a Pool: ../../rados/operations/pools#createpool
.. _Placement Groups: ../../rados/operations/placement-groups


Configure OpenStack Ceph Clients
================================

The hosts running ``glance-api``, ``nova-compute``, and ``nova-volume`` or
``cinder-volume`` act as Ceph clients. Each requires the ``ceph.conf`` file::

  ssh {your-openstack-server} sudo tee /etc/ceph/ceph.conf </etc/ceph/ceph.conf

Install Ceph client packages
----------------------------

On the ``glance-api`` host, you'll need the Python bindings for ``librbd``::

  sudo apt-get install python-ceph

On the ``nova-volume`` or ``cinder-volume`` host, use the client command line
tools::

  sudo apt-get install ceph-common


Setup Ceph Client Authentication
--------------------------------

If you have `cephx authentication`_ enabled, create a new user for Nova/Cinder
and Glance::

    ceph auth get-or-create client.volumes mon 'allow r' osd 'allow rwx pool=volumes, allow rx pool=images'
    ceph auth get-or-create client.images mon 'allow r' osd 'allow rwx pool=images'

Add the keyrings for ``client.volumes`` and ``client.images`` to the
appropriate hosts and change their ownership::

  ceph auth get-or-create client.images | ssh {your-glance-api-server} sudo tee /etc/ceph/ceph.client.images.keyring
  ssh {your-glance-api-server} sudo chown glance:glance /etc/ceph/ceph.client.images.keyring
  ceph auth get-or-create client.volumes | ssh {your-volume-server} sudo tee /etc/ceph/ceph.client.volumes.keyring
  ssh {your-volume-server} sudo chown cinder:cinder /etc/ceph/ceph.client.volumes.keyring

Hosts running ``nova-compute`` do not need the keyring. Instead, they
store the secret key in libvirt. Create a temporary copy of the secret
key on the hosts running ``nova-compute``::

  ssh {your-compute-host} client.volumes.key <`ceph auth get-key client.volumes`

Then, on the compute hosts, add the secret key to libvirt and remove
the temporary copy of the key::

  cat > secret.xml <<EOF
  <secret ephemeral='no' private='no'>
    <usage type='ceph'>
      <name>client.volumes secret</name>
    </usage>
  </secret>
  EOF
  sudo virsh secret-define --file secret.xml
  <uuid of secret is output here>
  sudo virsh secret-set-value --secret {uuid of secret} --base64 $(cat client.volumes.key) && rm client.volumes.key secret.xml

Save the uuid of the secret for configuring ``nova-compute`` later.

.. _cephx authentication: ../../rados/operations/authentication


Configure OpenStack to use Ceph
===============================

Configuring Glance
------------------

Glance can use multiple back ends to store images. To use Ceph block devices by
default, edit ``/etc/glance/glance-api.conf`` and add::

    default_store=rbd
    rbd_store_user=images
    rbd_store_pool=images

If you're using Folsom and want to enable copy-on-write cloning of
images into volumes, also add::

    show_image_direct_url=True

Note that this exposes the back end location via Glance's API, so the
endpoint with this option enabled should not be publicly accessible.


Configuring Cinder/nova-volume
------------------------------

OpenStack requires a driver to interact with Ceph block devices. You must also
specify the pool name for the block device. On your OpenStack host,
edit ``/etc/cinder/cinder.conf`` and add::

	volume_driver=cinder.volume.driver.RBDDriver
	rbd_pool=volumes

If you're not using Cinder, replace Cinder with Nova in the previous section.

If you're using `cephx authentication`_, also configure the user and
uuid of the secret you added to libvirt earlier::

    rbd_user=volumes
    rbd_secret_uuid={uuid of secret}

Finally, on each host running ``cinder-volume`` or ``nova-volume``, add
``CEPH_ARGS="--id volumes"`` to the init/upstart script that starts it.

For example, on Ubuntu, add ``env CEPH_ARGS="--id volumes"``
to the top of ``/etc/init/cinder-volume.conf``.


Restart OpenStack
=================

To activate the Ceph block device driver and load the block device pool name
into the configuration, you must restart OpenStack. Navigate the directory where
you installed OpenStack, and execute the following:: 

	./rejoin-stack.sh

If you have OpenStack configured as a service, you can also execute
these commands on the appropriate hosts::

    sudo service glance-api restart
    sudo service nova-compute restart
    sudo service cinder-volume restart

Once OpenStack is up and running, you should be able to create a volume with 
OpenStack on a Ceph block device.


Booting from a Block Device
===========================

If you're using OpenStack Folsom or later, you can create a volume from an image
using the Cinder command line tool::

    cinder create --image-id {id of image} --display-name {name of volume} {size of volume}

Note that image must be raw format. You can use `qemu-img`_ to convert
from one format to another, i.e.::

    qemu-img convert -f qcow2 -O raw precise-cloudimg.img precise-cloudimg.raw

Before Ceph 0.52 the image will be a full copy of the data. With Ceph 0.52 and
later when Glance and Cinder are both using Ceph block devices, the image is a
copy-on-write clone, so volume creation is very fast.

In the OpenStack dashboard you can then boot from that volume by launching a new
instance, choosing the image that you created the volume from, and selecting
'boot from volume' and the volume you created.

.. _qemu-img: ../qemu-rbd/#running-qemu-with-rbd