================================================= Configuring the Compute (nova) service (optional) ================================================= The Compute service (nova) handles the creation of virtual machines within an OpenStack environment. Many of the default options used by OpenStack-Ansible are found within ``defaults/main.yml`` within the nova role. Availability zones ~~~~~~~~~~~~~~~~~~ Deployers with multiple availability zones can set the ``nova_default_schedule_zone`` Ansible variable to specify an availability zone for new requests. This is useful in environments with different types of hypervisors, where builds are sent to certain hardware types based on their resource requirements. For example, if you have servers running on two racks without sharing the PDU. These two racks can be grouped into two availability zones. When one rack loses power, the other one still works. By spreading your containers onto the two racks (availability zones), you will improve your service availability. Block device tuning for Ceph (RBD) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Enabling Ceph and defining ``nova_libvirt_images_rbd_pool`` changes two libvirt configurations by default: * hw_disk_discard: ``unmap`` * disk_cachemodes: ``network=writeback`` Setting ``hw_disk_discard`` to ``unmap`` in libvirt enables discard (sometimes called TRIM) support for the underlying block device. This allows reclaiming of unused blocks on the underlying disks. Setting ``disk_cachemodes`` to ``network=writeback`` allows data to be written into a cache on each change, but those changes are flushed to disk at a regular interval. This can increase write performance on Ceph block devices. You have the option to customize these settings using two Ansible variables (defaults shown here): .. code-block:: yaml nova_libvirt_hw_disk_discard: 'unmap' nova_libvirt_disk_cachemodes: 'network=writeback' You can disable discard by setting ``nova_libvirt_hw_disk_discard`` to ``ignore``. The ``nova_libvirt_disk_cachemodes`` can be set to an empty string to disable ``network=writeback``. The following minimal example configuration sets nova to use the ``ephemeral-vms`` Ceph pool. The following example uses cephx authentication, and requires an existing ``cinder`` account for the ``ephemeral-vms`` pool: .. code-block:: console nova_libvirt_images_rbd_pool: ephemeral-vms ceph_mons: - 172.29.244.151 - 172.29.244.152 - 172.29.244.153 If you have a different Ceph username for the pool, use it as: .. code-block:: console cinder_ceph_client: * The `Ceph documentation for OpenStack`_ has additional information about these settings. * `OpenStack-Ansible and Ceph Working Example`_ .. _Ceph documentation for OpenStack: http://docs.ceph.com/docs/master/rbd/rbd-openstack/ .. _OpenStack-Ansible and Ceph Working Example: https://www.openstackfaq.com/openstack-ansible-ceph/ Config drive ~~~~~~~~~~~~ By default, OpenStack-Ansible does not configure nova to force config drives to be provisioned with every instance that nova builds. The metadata service provides configuration information that is used by ``cloud-init`` inside the instance. Config drives are only necessary when an instance does not have ``cloud-init`` installed or does not have support for handling metadata. A deployer can set an Ansible variable to force config drives to be deployed with every virtual machine: .. code-block:: yaml nova_force_config_drive: True Certain formats of config drives can prevent instances from migrating properly between hypervisors. If you need forced config drives and the ability to migrate instances, set the config drive format to ``vfat`` using the ``nova_nova_conf_overrides`` variable: .. code-block:: yaml nova_nova_conf_overrides: DEFAULT: config_drive_format: vfat force_config_drive: True Libvirtd connectivity and authentication ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ By default, OpenStack-Ansible configures the libvirt daemon in the following way: * TLS connections are enabled * TCP plaintext connections are disabled * Authentication over TCP connections uses SASL You can customize these settings using the following Ansible variables: .. code-block:: yaml # Enable libvirtd's TLS listener nova_libvirtd_listen_tls: 1 # Disable libvirtd's plaintext TCP listener nova_libvirtd_listen_tcp: 0 # Use SASL for authentication nova_libvirtd_auth_tcp: sasl Multipath ~~~~~~~~~ Nova supports multipath for iSCSI-based storage. Enable multipath support in nova through a configuration override: .. code-block:: yaml nova_nova_conf_overrides: libvirt: iscsi_use_multipath: true Shared storage and synchronized UID/GID ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Specify a custom UID for the nova user and GID for the nova group to ensure they are identical on each host. This is helpful when using shared storage on Compute nodes because it allows instances to migrate without filesystem ownership failures. By default, Ansible creates the nova user and group without specifying the UID or GID. To specify custom values for the UID or GID, set the following Ansible variables: .. code-block:: yaml nova_system_user_uid = nova_system_group_gid = .. warning:: Setting this value after deploying an environment with OpenStack-Ansible can cause failures, errors, and general instability. These values should only be set once before deploying an OpenStack environment and then never changed.