================================= Using libvirt with Ceph RBD ================================= .. index:: Ceph Block Device; livirt The ``libvirt`` library creates a virtual machine abstraction layer between hypervisor interfaces and the software applications that use them. With ``libvirt``, developers and system administrators can focus on a common management framework, common API, and common shell interface (i.e., ``virsh``) to many different hypervisors, including: - QEMU/KVM - XEN - LXC - VirtualBox - etc. Ceph block devices support QEMU/KVM. You can use Ceph block devices with software that interfaces with ``libvirt``. The following stack diagram illustrates how ``libvirt`` and QEMU use Ceph block devices via ``librbd``. .. ditaa:: +---------------------------------------------------+ | libvirt | +------------------------+--------------------------+ | | configures v +---------------------------------------------------+ | QEMU | +---------------------------------------------------+ | librbd | +------------------------+-+------------------------+ | OSDs | | Monitors | +------------------------+ +------------------------+ The most common ``libvirt`` use case involves providing Ceph block devices to cloud solutions like OpenStack or CloudStack. The cloud solution uses ``libvirt`` to interact with QEMU/KVM, and QEMU/KVM interacts with Ceph block devices via ``librbd``. See `Block Devices and OpenStack`_ and `Block Devices and CloudStack`_ for details. See `Installation`_ for installation details. You can also use Ceph block devices with ``libvirt``, ``virsh`` and the ``libvirt`` API. See `libvirt Virtualization API`_ for details. To create VMs that use Ceph block devices, use the procedures in the following sections. In the exemplary embodiment, we've used ``libvirt-pool`` for the pool name, ``client.libvirt`` for the user name, and ``new-libvirt-image`` for the image name. You may use any value you like, but ensure you replace those values when executing commands in the subsequent procedures. Configuring Ceph ================ To configure Ceph for use with ``libvirt``, perform the following steps: #. `Create a pool`_ (or use the default). The following example uses the pool name ``libvirt-pool`` with 128 placement groups. :: ceph osd pool create libvirt-pool 128 128 Verify the pool exists. :: ceph osd lspools #. `Create a Ceph User`_ (or use ``client.admin`` for version 0.9.7 and earlier). The following example uses the Ceph user name ``client.libvirt`` and references ``libvirt-pool``. :: ceph auth get-or-create client.libvirt mon 'allow r' osd 'allow class-read object_prefix rbd_children, allow rwx pool=libvirt-pool' Verify the name exists. :: ceph auth list **NOTE**: ``libvirt`` will access Ceph using the ID ``libvirt``, not the Ceph name ``client.libvirt``. See `User Management - User`_ and `User Management - CLI`_ for a detailed explanation of the difference between ID and name. #. Use QEMU to `create an image`_ in your RBD pool. The following example uses the image name ``new-libvirt-image`` and references ``libvirt-pool``. :: qemu-img create -f rbd rbd:libvirt-pool/new-libvirt-image 2G Verify the image exists. :: rbd -p libvirt-pool ls **NOTE:** You can also use `rbd create`_ to create an image, but we recommend ensuring that QEMU is working properly. .. tip:: Optionally, if you wish to enable debug logs and the admin socket for this client, you can add the following section to ``/etc/ceph/ceph.conf``:: [client.libvirt] log file = /var/log/ceph/qemu-guest-$pid.log admin socket = /var/run/ceph/$cluster-$type.$id.$pid.$cctid.asok The ``client.libvirt`` section name should match the cephx user you created above. If SELinux or AppArmor is enabled, note that this could prevent the client process (qemu via libvirt) from writing the logs or admin socket to the destination locations (``/var/log/ceph`` or ``/var/run/ceph``). Preparing the VM Manager ======================== You may use ``libvirt`` without a VM manager, but you may find it simpler to create your first domain with ``virt-manager``. #. Install a virtual machine manager. See `KVM/VirtManager`_ for details. :: sudo apt-get install virt-manager #. Download an OS image (if necessary). #. Launch the virtual machine manager. :: sudo virt-manager Creating a VM ============= To create a VM with ``virt-manager``, perform the following steps: #. Press the **Create New Virtual Machine** button. #. Name the new virtual machine domain. In the exemplary embodiment, we use the name ``libvirt-virtual-machine``. You may use any name you wish, but ensure you replace ``libvirt-virtual-machine`` with the name you choose in subsequent commandline and configuration examples. :: libvirt-virtual-machine #. Import the image. :: /path/to/image/recent-linux.img **NOTE:** Import a recent image. Some older images may not rescan for virtual devices properly. #. Configure and start the VM. #. You may use ``virsh list`` to verify the VM domain exists. :: sudo virsh list #. Login to the VM (root/root) #. Stop the VM before configuring it for use with Ceph. Configuring the VM ================== When configuring the VM for use with Ceph, it is important to use ``virsh`` where appropriate. Additionally, ``virsh`` commands often require root privileges (i.e., ``sudo``) and will not return appropriate results or notify you that that root privileges are required. For a reference of ``virsh`` commands, refer to `Virsh Command Reference`_. #. Open the configuration file with ``virsh edit``. :: sudo virsh edit {vm-domain-name} Under ```` there should be a ```` entry. :: /usr/bin/kvm
Replace ``/path/to/image/recent-linux.img`` with the path to the OS image. The minimum kernel for using the faster ``virtio`` bus is 2.6.25. See `Virtio`_ for details. **IMPORTANT:** Use ``sudo virsh edit`` instead of a text editor. If you edit the configuration file under ``/etc/libvirt/qemu`` with a text editor, ``libvirt`` may not recognize the change. If there is a discrepancy between the contents of the XML file under ``/etc/libvirt/qemu`` and the result of ``sudo virsh dumpxml {vm-domain-name}``, then your VM may not work properly. #. Add the Ceph RBD image you created as a ```` entry. :: Replace ``{monitor-host}`` with the name of your host, and replace the pool and/or image name as necessary. You may add multiple ```` entries for your Ceph monitors. The ``dev`` attribute is the logical device name that will appear under the ``/dev`` directory of your VM. The optional ``bus`` attribute indicates the type of disk device to emulate. The valid settings are driver specific (e.g., "ide", "scsi", "virtio", "xen", "usb" or "sata"). See `Disks`_ for details of the ```` element, and its child elements and attributes. #. Save the file. #. If your Ceph Storage Cluster has `Ceph Authentication`_ enabled (it does by default), you must generate a secret. :: cat > secret.xml < client.libvirt secret EOF #. Define the secret. :: sudo virsh secret-define --file secret.xml #. Get the ``client.libvirt`` key and save the key string to a file. :: ceph auth get-key client.libvirt | sudo tee client.libvirt.key #. Set the UUID of the secret. :: sudo virsh secret-set-value --secret {uuid of secret} --base64 $(cat client.libvirt.key) && rm client.libvirt.key secret.xml You must also set the secret manually by adding the following ```` entry to the ```` element you entered earlier (replacing the ``uuid`` value with the result from the command line example above). :: sudo virsh edit {vm-domain-name} Then, add ```` element to the domain configuration file:: ... `` appears under ``/dev`` or under ``proc/partitions``. :: ls dev cat proc/partitions If everything looks okay, you may begin using the Ceph block device within your VM. .. _Installation: ../../install .. _libvirt Virtualization API: http://www.libvirt.org .. _Block Devices and OpenStack: ../rbd-openstack .. _Block Devices and CloudStack: ../rbd-cloudstack .. _Create a pool: ../../rados/operations/pools#create-a-pool .. _Create a Ceph User: ../../rados/operations/user-management#add-a-user .. _create an image: ../qemu-rbd#creating-images-with-qemu .. _Virsh Command Reference: http://www.libvirt.org/virshcmdref.html .. _KVM/VirtManager: https://help.ubuntu.com/community/KVM/VirtManager .. _Ceph Authentication: ../../rados/configuration/auth-config-ref .. _Disks: http://www.libvirt.org/formatdomain.html#elementsDisks .. _rbd create: ../rados-rbd-cmds#creating-a-block-device-image .. _User Management - User: ../../rados/operations/user-management#user .. _User Management - CLI: ../../rados/operations/user-management#command-line-usage .. _Virtio: http://www.linux-kvm.org/page/Virtio