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219 lines
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219 lines
8.3 KiB
ReStructuredText
=============================
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Block Devices and OpenStack
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=============================
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You may use Ceph block device images with OpenStack through ``libvirt``, which
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configures the QEMU interface to ``librbd``. Ceph stripes block device images as
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objects across the cluster, which means that large Ceph block device images have
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better performance than a standalone server!
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To use Ceph block devices with OpenStack, you must install QEMU, ``libvirt``,
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and OpenStack first. We recommend using a separate physical host for your
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OpenStack installation. OpenStack recommends a minimum of 8GB of RAM and a
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quad-core processor. The following diagram depicts the OpenStack/Ceph
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technology stack.
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.. ditaa:: +---------------------------------------------------+
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| OpenStack |
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+---------------------------------------------------+
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| libvirt |
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+------------------------+--------------------------+
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| configures
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v
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+---------------------------------------------------+
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| QEMU |
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+---------------------------------------------------+
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| librbd |
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+---------------------------------------------------+
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| librados |
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+------------------------+-+------------------------+
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| OSDs | | Monitors |
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+------------------------+ +------------------------+
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.. important:: To use Ceph block devices with OpenStack, you must have a running Ceph cluster.
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Two parts of OpenStack integrate with Ceph's block devices:
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- **Images**: OpenStack Glance manages images for VMs. Images
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are immutable. OpenStack treats images as binary blobs and
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downloads them accordingly.
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- **Volumes**: Volumes are block devices. OpenStack uses volumes
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to boot VMs, or to attach volumes to running VMs. OpenStack
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manages volumes using ``nova-volume`` prior to the Folsom
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release. OpenStack manages volumes using Cinder services
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beginning with the Folsom release.
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Beginning with OpenStack Folsom and Ceph 0.52, you can use OpenStack Glance to
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store images in a Ceph block device, and you can use Cinder or ``nova-volume``
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to boot a VM using a copy-on-write clone of an image.
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The instructions below detail the setup for Glance and Nova/Cinder, although
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they do not have to be used together. You may store images in Ceph block devices
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while running VMs using a local disk, or vice versa.
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Create a Pool
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=============
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By default, Ceph block devices use the ``rbd`` pool. You may use any available
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pool. We recommend creating a pool for Nova/Cinder and a pool for Glance. Ensure
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your Ceph cluster is running, then create the pools. ::
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ceph osd pool create volumes
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ceph osd pool create images
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See `Create a Pool`_ for detail on specifying the number of placement groups for
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your pools, and `Placement Groups`_ for details on the number of placement
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groups you should set for your pools.
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If you have `cephx authentication`_ enabled, create a new user for Nova/Cinder
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and Glance::
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ceph auth get-or-create client.volumes mon 'allow r' osd 'allow rwx pool=volumes, allow rx pool=images'
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ceph auth get-or-create client.images mon 'allow r' osd 'allow rwx pool=images'
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.. _Create a Pool: ../../cluster-ops/pools#createpool
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.. _Placement Groups: ../../cluster-ops/placement-groups
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.. _cephx authentication: ../../cluster-ops/authentication
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Configure OpenStack Ceph Clients
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================================
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The hosts running ``glance-api``, ``nova-compute``, and ``nova-volume`` or
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``cinder-volume`` act as Ceph clients. Each requires the ``ceph.conf`` file::
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ssh {your-openstack-server} sudo tee /etc/ceph/ceph.conf </etc/ceph/ceph.conf
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Install Ceph client packages
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----------------------------
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On the ``glance-api`` host, you'll need the Python bindings for ``librbd``::
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sudo apt-get install python-ceph
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On the ``nova-volume`` or ``cinder-volume`` host, use the client command line
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tools::
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sudo apt-get install ceph-common
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Setup Ceph Client Authentication
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--------------------------------
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If you're using cephx authentication, add the keyrings for ``client.volumes``
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and ``client.images`` to the appropriate hosts and change their ownership::
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ceph auth get-or-create client.images | ssh {your-glance-api-server} sudo tee /etc/ceph/ceph.client.images.keyring
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ssh {your-glance-api-server} sudo chown glance:glance /etc/ceph/ceph.client.images.keyring
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ceph auth get-or-create client.volumes | ssh {your-volume-server} sudo tee /etc/ceph/ceph.client.volumes.keyring
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ssh {your-volume-server} sudo chown cinder:cinder /etc/ceph/ceph.client.volumes.keyring
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Hosts running ``nova-compute`` do not need the keyring. Instead, they
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store the secret key in libvirt. Create a temporary copy of the secret
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key on the hosts running ``nova-compute``::
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ssh {your-compute-host} client.volumes.key <`ceph auth get-key client.volumes`
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Then, on the compute hosts, add the secret key to libvirt and remove
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the temporary copy of the key::
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cat > secret.xml <<EOF
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<secret ephemeral='no' private='no'>
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<usage type='ceph'>
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<name>client.volumes secret</name>
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</usage>
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</secret>
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EOF
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sudo virsh secret-define --file secret.xml
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<uuid of secret is output here>
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sudo virsh secret-set-value --secret {uuid of secret} --base64 $(cat client.volumes.key) && rm client.volumes.key secret.xml
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Save the uuid of the secret for configuring ``nova-compute`` later.
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Finally, on each host running ``cinder-volume`` or ``nova-volume``, add
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``CEPH_ARGS="--id volumes"`` to the init/upstart script that starts it.
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For example, on Ubuntu, add ``env CEPH_ARGS="--id volumes"``
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to the top of ``/etc/init/cinder-volume``.
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Configure OpenStack to use Ceph
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===============================
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Configuring Glance
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------------------
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Glance can use multiple back ends to store images. To use Ceph block devices by
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default, edit ``/etc/glance/glance-api.conf`` and add::
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default_store=rbd
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rbd_store_user=images
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rbd_store_pool=images
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If you're using Folsom and want to enable copy-on-write cloning of
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images into volumes, also add::
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show_image_direct_url=True
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Note that this exposes the back end location via Glance's API, so the
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endpoint with this option enabled should not be publicly accessible.
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Configuring Cinder/nova-volume
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------------------------------
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OpenStack requires a driver to interact with Ceph block devices. You must also
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specify the pool name for the block device. On your OpenStack host,
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edit ``/etc/cinder/cinder.conf`` and add::
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volume_driver=cinder.volume.driver.RBDDriver
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rbd_pool=volumes
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If you're not using Cinder, replace Cinder with Nova in the previous section.
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If you're using `cephx authentication`_, also configure the user and
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uuid of the secret you added to libvirt earlier::
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rbd_user=volumes
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rbd_secret_uuid={uuid of secret}
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Restart OpenStack
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=================
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To activate the Ceph block device driver and load the block device pool name
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into the configuration, you must restart OpenStack. Navigate the directory where
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you installed OpenStack, and execute the following::
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./rejoin-stack.sh
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If you have OpenStack configured as a service, you can also execute
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these commands on the appropriate hosts::
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sudo service glance-api restart
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sudo service nova-compute restart
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sudo service cinder-volume restart
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Once OpenStack is up and running, you should be able to create a volume with
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OpenStack on a Ceph block device.
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Booting from a Block Device
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===========================
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If you're using OpenStack Folsom or later, you can create a volume from an image
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using the Cinder command line tool::
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cinder create --image-id {id of image} --display-name {name of volume} {size of volume}
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Before Ceph 0.52 the image will be a full copy of the data. With Ceph 0.52 and
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later when Glance and Cinder are both using Ceph block devices, the image is a
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copy-on-write clone, so volume creation is very fast.
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In the OpenStack dashboard you can then boot from that volume by launching a new
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instance, choosing the image that you created the volume from, and selecting
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'boot from volume' and the volume you created.
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