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396 lines
15 KiB
ReStructuredText
=============================
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Block Devices and OpenStack
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=============================
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.. index:: Ceph Block Device; OpenStack
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You can attach Ceph Block Device images to OpenStack instances through ``libvirt``,
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which configures the QEMU interface to ``librbd``. Ceph stripes block volumes
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across multiple OSDs within the cluster, which means that large volumes can
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realize better performance than local drives on 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 node 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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+---------------------------------------------------+
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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
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access to a running Ceph Storage Cluster.
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Three parts of OpenStack integrate with Ceph's block devices:
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- **Images**: OpenStack Glance manages images for VMs. Images are immutable.
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OpenStack treats images as binary blobs and downloads them accordingly.
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- **Volumes**: Volumes are block devices. OpenStack uses volumes to boot VMs,
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or to attach volumes to running VMs. OpenStack manages volumes using
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Cinder services.
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- **Guest Disks**: Guest disks are guest operating system disks. By default,
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when you boot a virtual machine, its disk appears as a file on the file system
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of the hypervisor (usually under ``/var/lib/nova/instances/<uuid>/``). Prior
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to OpenStack Havana, the only way to boot a VM in Ceph was to use the
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boot-from-volume functionality of Cinder. However, now it is possible to boot
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every virtual machine inside Ceph directly without using Cinder, which is
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advantageous because it allows you to perform maintenance operations easily
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with the live-migration process. Additionally, if your hypervisor dies it is
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also convenient to trigger ``nova evacuate`` and reinstate the virtual machine
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elsewhere almost seamlessly. In doing so,
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:ref:`exclusive locks <rbd-exclusive-locks>` prevent multiple
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compute nodes from concurrently accessing the guest disk.
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You can use OpenStack Glance to store images as Ceph Block Devices, and you
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can use Cinder 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, Cinder and Nova, 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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.. important:: Using QCOW2 for hosting a virtual machine disk is NOT recommended.
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If you want to boot virtual machines in Ceph (ephemeral backend or boot
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from volume), please use the ``raw`` image format within Glance.
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.. index:: pools; OpenStack
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Create a Pool
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=============
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By default, Ceph block devices live within the ``rbd`` pool. You may use any
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suitable pool by specifying it explicitly. We recommend creating a pool for
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Cinder and a pool for Glance. Ensure 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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ceph osd pool create backups
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ceph osd pool create vms
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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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Newly created pools must be initialized prior to use. Use the ``rbd`` tool
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to initialize the pools::
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rbd pool init volumes
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rbd pool init images
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rbd pool init backups
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rbd pool init vms
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.. _Create a Pool: ../../rados/operations/pools#createpool
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.. _Placement Groups: ../../rados/operations/placement-groups
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Configure OpenStack Ceph Clients
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================================
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The nodes running ``glance-api``, ``cinder-volume``, ``nova-compute`` and
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``cinder-backup`` 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`` node, you will need the Python bindings for ``librbd``::
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sudo apt-get install python-rbd
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sudo yum install python-rbd
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On the ``nova-compute``, ``cinder-backup`` and on the ``cinder-volume`` node,
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use both the Python bindings and the client command line tools::
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sudo apt-get install ceph-common
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sudo yum install ceph-common
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Setup Ceph Client Authentication
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--------------------------------
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If you have `cephx authentication`_ enabled, create a new user for Nova/Cinder
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and Glance. Execute the following::
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ceph auth get-or-create client.glance mon 'profile rbd' osd 'profile rbd pool=images' mgr 'profile rbd pool=images'
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ceph auth get-or-create client.cinder mon 'profile rbd' osd 'profile rbd pool=volumes, profile rbd pool=vms, profile rbd-read-only pool=images' mgr 'profile rbd pool=volumes, profile rbd pool=vms'
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ceph auth get-or-create client.cinder-backup mon 'profile rbd' osd 'profile rbd pool=backups' mgr 'profile rbd pool=backups'
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Add the keyrings for ``client.cinder``, ``client.glance``, and
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``client.cinder-backup`` to the appropriate nodes and change their ownership::
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ceph auth get-or-create client.glance | ssh {your-glance-api-server} sudo tee /etc/ceph/ceph.client.glance.keyring
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ssh {your-glance-api-server} sudo chown glance:glance /etc/ceph/ceph.client.glance.keyring
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ceph auth get-or-create client.cinder | ssh {your-volume-server} sudo tee /etc/ceph/ceph.client.cinder.keyring
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ssh {your-cinder-volume-server} sudo chown cinder:cinder /etc/ceph/ceph.client.cinder.keyring
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ceph auth get-or-create client.cinder-backup | ssh {your-cinder-backup-server} sudo tee /etc/ceph/ceph.client.cinder-backup.keyring
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ssh {your-cinder-backup-server} sudo chown cinder:cinder /etc/ceph/ceph.client.cinder-backup.keyring
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Nodes running ``nova-compute`` need the keyring file for the ``nova-compute``
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process::
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ceph auth get-or-create client.cinder | ssh {your-nova-compute-server} sudo tee /etc/ceph/ceph.client.cinder.keyring
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They also need to store the secret key of the ``client.cinder`` user in
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``libvirt``. The libvirt process needs it to access the cluster while attaching
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a block device from Cinder.
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Create a temporary copy of the secret key on the nodes running
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``nova-compute``::
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ceph auth get-key client.cinder | ssh {your-compute-node} tee client.cinder.key
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Then, on the compute nodes, add the secret key to ``libvirt`` and remove the
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temporary copy of the key::
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uuidgen
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457eb676-33da-42ec-9a8c-9293d545c337
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cat > secret.xml <<EOF
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<secret ephemeral='no' private='no'>
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<uuid>457eb676-33da-42ec-9a8c-9293d545c337</uuid>
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<usage type='ceph'>
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<name>client.cinder 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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Secret 457eb676-33da-42ec-9a8c-9293d545c337 created
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sudo virsh secret-set-value --secret 457eb676-33da-42ec-9a8c-9293d545c337 --base64 $(cat client.cinder.key) && rm client.cinder.key secret.xml
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Save the uuid of the secret for configuring ``nova-compute`` later.
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.. important:: You don't necessarily need the UUID on all the compute nodes.
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However from a platform consistency perspective, it's better to keep the
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same UUID.
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.. _cephx authentication: ../../rados/configuration/auth-config-ref/#enabling-disabling-cephx
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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, configure Glance like the following.
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Kilo and after
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~~~~~~~~~~~~~~
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Edit ``/etc/glance/glance-api.conf`` and add under the ``[glance_store]`` section::
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[glance_store]
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stores = rbd
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default_store = rbd
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rbd_store_pool = images
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rbd_store_user = glance
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rbd_store_ceph_conf = /etc/ceph/ceph.conf
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rbd_store_chunk_size = 8
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For more information about the configuration options available in Glance please refer to the OpenStack Configuration Reference: http://docs.openstack.org/.
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Enable copy-on-write cloning of images
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Note that this exposes the back end location via Glance's API, so the endpoint
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with this option enabled should not be publicly accessible.
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Any OpenStack version except Mitaka
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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If you want to enable copy-on-write cloning of images, also add under the ``[DEFAULT]`` section::
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show_image_direct_url = True
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Disable cache management (any OpenStack version)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Disable the Glance cache management to avoid images getting cached under ``/var/lib/glance/image-cache/``,
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assuming your configuration file has ``flavor = keystone+cachemanagement``::
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[paste_deploy]
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flavor = keystone
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Image properties
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~~~~~~~~~~~~~~~~
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We recommend to use the following properties for your images:
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- ``hw_scsi_model=virtio-scsi``: add the virtio-scsi controller and get better performance and support for discard operation
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- ``hw_disk_bus=scsi``: connect every cinder block devices to that controller
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- ``hw_qemu_guest_agent=yes``: enable the QEMU guest agent
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- ``os_require_quiesce=yes``: send fs-freeze/thaw calls through the QEMU guest agent
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Configuring Cinder
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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 node, edit
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``/etc/cinder/cinder.conf`` by adding::
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[DEFAULT]
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...
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enabled_backends = ceph
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glance_api_version = 2
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...
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[ceph]
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volume_driver = cinder.volume.drivers.rbd.RBDDriver
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volume_backend_name = ceph
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rbd_pool = volumes
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rbd_ceph_conf = /etc/ceph/ceph.conf
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rbd_flatten_volume_from_snapshot = false
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rbd_max_clone_depth = 5
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rbd_store_chunk_size = 4
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rados_connect_timeout = -1
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If you are using `cephx authentication`_, also configure the user and uuid of
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the secret you added to ``libvirt`` as documented earlier::
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[ceph]
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...
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rbd_user = cinder
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rbd_secret_uuid = 457eb676-33da-42ec-9a8c-9293d545c337
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Note that if you are configuring multiple cinder back ends,
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``glance_api_version = 2`` must be in the ``[DEFAULT]`` section.
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Configuring Cinder Backup
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-------------------------
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OpenStack Cinder Backup requires a specific daemon so don't forget to install it.
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On your Cinder Backup node, edit ``/etc/cinder/cinder.conf`` and add::
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backup_driver = cinder.backup.drivers.ceph
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backup_ceph_conf = /etc/ceph/ceph.conf
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backup_ceph_user = cinder-backup
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backup_ceph_chunk_size = 134217728
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backup_ceph_pool = backups
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backup_ceph_stripe_unit = 0
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backup_ceph_stripe_count = 0
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restore_discard_excess_bytes = true
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Configuring Nova to attach Ceph RBD block device
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------------------------------------------------
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In order to attach Cinder devices (either normal block or by issuing a boot
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from volume), you must tell Nova (and libvirt) which user and UUID to refer to
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when attaching the device. libvirt will refer to this user when connecting and
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authenticating with the Ceph cluster. ::
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[libvirt]
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...
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rbd_user = cinder
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rbd_secret_uuid = 457eb676-33da-42ec-9a8c-9293d545c337
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These two flags are also used by the Nova ephemeral back end.
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Configuring Nova
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----------------
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In order to boot virtual machines directly from Ceph volumes, you must
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configure the ephemeral backend for Nova.
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It is recommended to enable the RBD cache in your Ceph configuration file; this
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has been enabled by default since the Giant release. Moreover, enabling the
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client admin socket allows the collection of metrics and can be invaluable
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for troubleshooting.
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This socket can be accessed on the hypvervisor (Nova compute) node::
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ceph daemon /var/run/ceph/ceph-client.cinder.19195.32310016.asok help
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To enable RBD cache and admin sockets, ensure that on each hypervisor's
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``ceph.conf`` contains::
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[client]
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rbd cache = true
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rbd cache writethrough until flush = true
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admin socket = /var/run/ceph/guests/$cluster-$type.$id.$pid.$cctid.asok
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log file = /var/log/qemu/qemu-guest-$pid.log
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rbd concurrent management ops = 20
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Configure permissions for these directories::
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mkdir -p /var/run/ceph/guests/ /var/log/qemu/
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chown qemu:libvirtd /var/run/ceph/guests /var/log/qemu/
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Note that user ``qemu`` and group ``libvirtd`` can vary depending on your system.
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The provided example works for RedHat based systems.
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.. tip:: If your virtual machine is already running you can simply restart it to enable the admin socket
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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 the related OpenStack services.
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For Debian based systems execute these commands on the appropriate nodes::
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sudo glance-control api restart
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sudo service nova-compute restart
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sudo service cinder-volume restart
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sudo service cinder-backup restart
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For Red Hat based systems execute::
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sudo service openstack-glance-api restart
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sudo service openstack-nova-compute restart
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sudo service openstack-cinder-volume restart
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sudo service openstack-cinder-backup restart
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Once OpenStack is up and running, you should be able to create a volume
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and boot from it.
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Booting from a Block Device
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===========================
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You can create a volume from an image 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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You can use `qemu-img`_ to convert from one format to another. For example::
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qemu-img convert -f {source-format} -O {output-format} {source-filename} {output-filename}
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qemu-img convert -f qcow2 -O raw precise-cloudimg.img precise-cloudimg.raw
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When Glance and Cinder are both using Ceph block devices, the image is a
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copy-on-write clone, so new volumes are created quickly. In the OpenStack
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dashboard, you can boot from that volume by performing the following steps:
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#. Launch a new instance.
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#. Choose the image associated to the copy-on-write clone.
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#. Select 'boot from volume'.
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#. Select the volume you created.
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.. _qemu-img: ../qemu-rbd/#running-qemu-with-rbd
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