Home OpenStack-Ansible Installation Guide
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.
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.
Enabling Ceph and defining nova_libvirt_images_rbd_pool changes two libvirt configurations by default:
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):
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:
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:
cinder_ceph_client: <ceph-username>
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:
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:
nova_nova_conf_overrides:
DEFAULT:
config_drive_format: vfat
force_config_drive: True
By default, OpenStack-Ansible configures the libvirt daemon in the following way:
You can customize these settings using the following Ansible variables:
# 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
Nova supports multipath for iSCSI-based storage. Enable multipath support in nova through a configuration override:
nova_nova_conf_overrides:
libvirt:
iscsi_use_multipath: true