Patch fixes titles for doc files and resolves naming problems Change-Id: I7ceca25d48801c79348e23ca7c8a65db0a6daf4e
5.5 KiB
Configuring the Compute (zun) service (optional)
The Compute service (zun) 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 zun role.
Availability zones
Deployers with multiple availability zones can set the
zun_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 zun_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):
zun_libvirt_hw_disk_discard: 'unmap'
zun_libvirt_disk_cachemodes: 'network=writeback'
You can disable discard by setting
zun_libvirt_hw_disk_discard
to ignore
. The
zun_libvirt_disk_cachemodes
can be set to an empty string
to disable network=writeback
.
The following minimal example configuration sets zun to use the
ephemeral-vms
Ceph pool. The following example uses cephx
authentication, and requires an existing cinder
account for
the ephemeral-vms
pool:
zun_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>
- The Ceph documentation for OpenStack has additional information about these settings.
- OpenStack-Ansible and Ceph Working Example
Config drive
By default, OpenStack-Ansible does not configure zun to force config
drives to be provisioned with every instance that zun 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:
zun_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 zun_zun_conf_overrides
variable:
zun_zun_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:
# Enable libvirtd's TLS listener
zun_libvirtd_listen_tls: 1
# Disable libvirtd's plaintext TCP listener
zun_libvirtd_listen_tcp: 0
# Use SASL for authentication
zun_libvirtd_auth_tcp: sasl
Multipath
Nova supports multipath for iSCSI-based storage. Enable multipath support in zun through a configuration override:
zun_zun_conf_overrides:
libvirt:
iscsi_use_multipath: true
Shared storage and synchronized UID/GID
Specify a custom UID for the zun user and GID for the zun 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 zun user and group without specifying the UID or GID. To specify custom values for the UID or GID, set the following Ansible variables:
zun_system_user_uid = <specify a UID>
zun_system_group_gid = <specify a 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.