ceph/doc/rbd/rbd-openstack.rst

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

.. index:: Ceph Block Device; 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 node 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 
   access to a running Ceph Storage 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 Cinder services.

You can use  OpenStack Glance to store images in a Ceph Block Device, and you
can use Cinder to boot a VM using a copy-on-write clone of an image.

The instructions below detail the setup for Glance and 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.

.. tip:: This document describes using Ceph Block Devices with OpenStack Havana. 
   For earlier versions of OpenStack see 
   `Block Devices and OpenStack (Dumpling)`_.

.. index:: pools; OpenStack

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

By default, Ceph block devices use the ``rbd`` pool. You may use any available
pool. We recommend creating a pool for 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 nodes running ``glance-api`` and ``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`` node and on the ``cinder-volume`` node, you'll need the
Python bindings for ``librbd``::

  sudo apt-get install python-ceph
  sudo yum install python-ceph

On the ``cinder-volume`` node, use the client command line tools::

  sudo apt-get install ceph-common
  sudo yum install ceph


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

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

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

Add the keyrings for ``client.volumes`` and ``client.images`` to the appropriate
nodes 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

Nodes 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 nodes running ``nova-compute``::

  ceph auth get-key client.volumes | ssh {your-compute-node} tee client.volumes.key 

Then, on the compute nodes, 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
------------------

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

    volume_driver=cinder.volume.drivers.rbd.RBDDriver
    rbd_pool=volumes
    glance_api_version=2

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}



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 nodes::

    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
===========================

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

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
.. _Block Devices and OpenStack (Dumpling): http://ceph.com/docs/dumpling/rbd/rbd-openstack