=============================
 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.

Three 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.

- **Guest Disks**: Guest disks are guest operating system disks. By default,
  when you boot a virtual machine, its disk appears as a file on the filesystem
  of the hypervisor (usually under ``/var/lib/nova/instances/<uuid>/``). Prior
  to OpenStack Havana, the only way to boot a VM in Ceph was to use the
  boot-from-volume functionality of Cinder. However, now it is possible to boot
  every virtual machine inside Ceph directly without using Cinder, which is
  advantageous because it allows you to perform maintenance operations easily
  with the live-migration process. Additionally, if your hypervisor dies it is
  also convenient to trigger ``nova evacuate`` and  run the virtual machine
  elsewhere almost seamlessly.

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, Cinder and Nova, 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.

.. important:: Ceph doesn’t support QCOW2 for hosting a virtual machine disk.
   Thus if you want to boot virtual machines in Ceph (ephemeral backend or boot
   from volume), the Glance image format must be ``RAW``.

.. 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
    ceph osd pool create backups 128
    ceph osd pool create vms 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``, ``cinder-volume``, ``nova-compute`` and
``cinder-backup`` 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, you'll need the Python bindings for ``librbd``::

  sudo apt-get install python-rbd
  sudo yum install python-rbd

On the ``nova-compute``, ``cinder-backup`` and on the ``cinder-volume`` node,
use both the Python bindings and the client command line tools::

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


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

Add the keyrings for ``client.cinder``, ``client.glance``, and
``client.cinder-backup`` to the appropriate nodes and change their ownership::

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

Nodes running ``nova-compute`` need the keyring file for the ``nova-compute``
process::

  ceph auth get-or-create client.cinder | ssh {your-nova-compute-server} sudo tee /etc/ceph/ceph.client.cinder.keyring

They also need to store the secret key of the ``client.cinder`` user in
``libvirt``. The libvirt process needs it to access the cluster while attaching
a block device from Cinder.

Create a temporary copy of the secret key on the nodes running
``nova-compute``::

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

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

  uuidgen
  457eb676-33da-42ec-9a8c-9293d545c337

  cat > secret.xml <<EOF
  <secret ephemeral='no' private='no'>
    <uuid>457eb676-33da-42ec-9a8c-9293d545c337</uuid>
    <usage type='ceph'>
      <name>client.cinder secret</name>
    </usage>
  </secret>
  EOF
  sudo virsh secret-define --file secret.xml
  Secret 457eb676-33da-42ec-9a8c-9293d545c337 created
  sudo virsh secret-set-value --secret 457eb676-33da-42ec-9a8c-9293d545c337 --base64 $(cat client.cinder.key) && rm client.cinder.key secret.xml

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

.. important:: You don't necessarily need the UUID on all the compute nodes.
   However from a platform consistency perspective, it's better to keep the
   same UUID.

.. _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, configure Glance like the following.

Prior to Juno
~~~~~~~~~~~~~~

Edit ``/etc/glance/glance-api.conf`` and add under the ``[DEFAULT]`` section::

    default_store = rbd
    rbd_store_user = glance
    rbd_store_pool = images
    rbd_store_chunk_size = 8


Juno
~~~~

Edit ``/etc/glance/glance-api.conf`` and add under the ``[glance_store]`` section::

    [DEFAULT]
    ...
    default_store = rbd
    ...
    [glance_store]
    stores = rbd
    rbd_store_pool = images
    rbd_store_user = glance
    rbd_store_ceph_conf = /etc/ceph/ceph.conf
    rbd_store_chunk_size = 8


For more information about the configuration options available in Glance please see: http://docs.openstack.org/trunk/config-reference/content/section_glance-api.conf.html.

.. important:: Glance has not completely moved to 'store' yet.
    So we still need to configure the store in the DEFAULT section.

Any OpenStack version
~~~~~~~~~~~~~~~~~~~~~

If you want to enable copy-on-write cloning of images, also add under the ``[DEFAULT]`` section::

    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.

Disable the Glance cache management to avoid images getting cached under ``/var/lib/glance/image-cache/``,
assuming your configuration file has ``flavor = keystone+cachemanagement``::

    [paste_deploy]
    flavor = keystone

Image properties
~~~~~~~~~~~~~~~~

We recommend to use the following properties for your images:

- ``hw_scsi_model=virtio-scsi``: add the virtio-scsi controller and get better performance and support for discard operation
- ``hw_disk_bus=scsi``: connect every cinder block devices to that controller
- ``hw_qemu_guest_agent=yes``: enable the QEMU guest agent
- ``os_require_quiesce=yes``: send fs-freeze/thaw calls through the QEMU guest agent


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::

    [DEFAULT]
    ...
    enabled_backends = ceph
    ...
    [ceph]
    volume_driver = cinder.volume.drivers.rbd.RBDDriver
    rbd_pool = volumes
    rbd_ceph_conf = /etc/ceph/ceph.conf
    rbd_flatten_volume_from_snapshot = false
    rbd_max_clone_depth = 5
    rbd_store_chunk_size = 4
    rados_connect_timeout = -1
    glance_api_version = 2

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

    [ceph]
    ...
    rbd_user = cinder
    rbd_secret_uuid = 457eb676-33da-42ec-9a8c-9293d545c337

Note that if you are configuring multiple cinder back ends,
``glance_api_version = 2`` must be in the ``[DEFAULT]`` section.


Configuring Cinder Backup
-------------------------

OpenStack Cinder Backup requires a specific daemon so don't forget to install it.
On your Cinder Backup node, edit ``/etc/cinder/cinder.conf`` and add::

    backup_driver = cinder.backup.drivers.ceph
    backup_ceph_conf = /etc/ceph/ceph.conf
    backup_ceph_user = cinder-backup
    backup_ceph_chunk_size = 134217728
    backup_ceph_pool = backups
    backup_ceph_stripe_unit = 0
    backup_ceph_stripe_count = 0
    restore_discard_excess_bytes = true


Configuring Nova to attach Ceph RBD block device
------------------------------------------------

In order to attach Cinder devices (either normal block or by issuing a boot
from volume), you must tell Nova (and libvirt) which user and UUID to refer to
when attaching the device. libvirt will refer to this user when connecting and
authenticating with the Ceph cluster. ::

    rbd_user = cinder
    rbd_secret_uuid = 457eb676-33da-42ec-9a8c-9293d545c337

These two flags are also used by the Nova ephemeral backend.


Configuring Nova
----------------

In order to boot all the virtual machines directly into Ceph, you must
configure the ephemeral backend for Nova.

It is recommended to enable the RBD cache in your Ceph configuration file
(enabled by default since Giant). Moreover, enabling the admin socket
brings a lot of benefits while troubleshooting. Having one socket
per virtual machine using a Ceph block device will help investigating performance and/or wrong behaviors.

This socket can be accessed like this::

    ceph daemon /var/run/ceph/ceph-client.cinder.19195.32310016.asok help

Now on every compute nodes edit your Ceph configuration file::

    [client]
        rbd cache = true
        rbd cache writethrough until flush = true
        admin socket = /var/run/ceph/guests/$cluster-$type.$id.$pid.$cctid.asok
        log file = /var/log/qemu/qemu-guest-$pid.log
        rbd concurrent management ops = 20

Configure the permissions of these paths::

    mkdir -p /var/run/ceph/guests/ /var/log/qemu/
    chown qemu:libvirtd /var/run/ceph/guests /var/log/qemu/

Note that user ``qemu`` and group ``libvirtd`` can vary depending on your system.
The provided example works for RedHat based systems.

.. tip:: If your virtual machine is already running you can simply restart it to get the socket


Havana and Icehouse
~~~~~~~~~~~~~~~~~~~

Havana and Icehouse require patches to implement copy-on-write cloning and fix
bugs with image size and live migration of ephemeral disks on rbd. These are
available in branches based on upstream Nova `stable/havana`_  and
`stable/icehouse`_. Using them is not mandatory but **highly recommended** in
order to take advantage of the copy-on-write clone functionality.

On every Compute node, edit ``/etc/nova/nova.conf`` and add::

    libvirt_images_type = rbd
    libvirt_images_rbd_pool = vms
    libvirt_images_rbd_ceph_conf = /etc/ceph/ceph.conf
    libvirt_disk_cachemodes="network=writeback"
    rbd_user = cinder
    rbd_secret_uuid = 457eb676-33da-42ec-9a8c-9293d545c337

It is also a good practice to disable file injection. While booting an
instance, Nova usually attempts to open the rootfs of the virtual machine.
Then, Nova injects values such as password, ssh keys etc. directly into the
filesystem. However, it is better to rely on the metadata service and
``cloud-init``.

On every Compute node, edit ``/etc/nova/nova.conf`` and add::

    libvirt_inject_password = false
    libvirt_inject_key = false
    libvirt_inject_partition = -2

To ensure a proper live-migration, use the following flags::

    libvirt_live_migration_flag="VIR_MIGRATE_UNDEFINE_SOURCE,VIR_MIGRATE_PEER2PEER,VIR_MIGRATE_LIVE,VIR_MIGRATE_PERSIST_DEST,VIR_MIGRATE_TUNNELLED"

Juno
~~~~

In Juno, Ceph block device was moved under the ``[libvirt]`` section.
On every Compute node, edit ``/etc/nova/nova.conf`` under the ``[libvirt]``
section and add::

    [libvirt]
    images_type = rbd
    images_rbd_pool = vms
    images_rbd_ceph_conf = /etc/ceph/ceph.conf
    rbd_user = cinder
    rbd_secret_uuid = 457eb676-33da-42ec-9a8c-9293d545c337
    disk_cachemodes="network=writeback"


It is also a good practice to disable file injection. While booting an
instance, Nova usually attempts to open the rootfs of the virtual machine.
Then, Nova injects values such as password, ssh keys etc. directly into the
filesystem. However, it is better to rely on the metadata service and
``cloud-init``.

On every Compute node, edit ``/etc/nova/nova.conf`` and add the following
under the ``[libvirt]`` section::

    inject_password = false
    inject_key = false
    inject_partition = -2

To ensure a proper live-migration, use the following flags (under the ``[libvirt]`` section)::

    live_migration_flag="VIR_MIGRATE_UNDEFINE_SOURCE,VIR_MIGRATE_PEER2PEER,VIR_MIGRATE_LIVE,VIR_MIGRATE_PERSIST_DEST,VIR_MIGRATE_TUNNELLED"

Kilo
~~~~

Enable discard support for virtual machine ephemeral root disk::

    [libvirt]
    ...
    ...
    hw_disk_discard = unmap # enable discard support (be careful of performance)


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

To activate the Ceph block device driver and load the block device pool name
into the configuration, you must restart OpenStack. Thus, for Debian based
systems execute these commands on the appropriate nodes::

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

For Red Hat based systems execute::

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

Once OpenStack is up and running, you should be able to create a volume
and boot from it.


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. For example::

    qemu-img convert -f {source-format} -O {output-format} {source-filename} {output-filename}
    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 it can create a new volume quickly. In the OpenStack
dashboard, you can boot from that volume by performing the following steps:

#. Launch a new instance.
#. Choose the image associated to the copy-on-write clone.
#. Select 'boot from volume'.
#. Select 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
.. _stable/havana: https://github.com/jdurgin/nova/tree/havana-ephemeral-rbd
.. _stable/icehouse: https://github.com/angdraug/nova/tree/rbd-ephemeral-clone-stable-icehouse