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