================== Compute schedulers ================== Compute uses the ``nova-scheduler`` service to determine how to dispatch compute requests. For example, the ``nova-scheduler`` service determines on which host a VM should launch. In the context of filters, the term ``host`` means a physical node that has a ``nova-compute`` service running on it. You can configure the scheduler through a variety of options. Compute is configured with the following default scheduler options in the ``/etc/nova/nova.conf`` file: .. code-block:: ini [scheduler] driver = filter_scheduler [filter_scheduler] available_filters = nova.scheduler.filters.all_filters enabled_filters = RetryFilter, AvailabilityZoneFilter, ComputeFilter, ComputeCapabilitiesFilter, ImagePropertiesFilter, ServerGroupAntiAffinityFilter, ServerGroupAffinityFilter By default, the scheduler ``driver`` is configured as a filter scheduler, as described in the next section. In the default configuration, this scheduler considers hosts that meet all the following criteria: * Have not been attempted for scheduling purposes (``RetryFilter``). * Are in the requested availability zone (``AvailabilityZoneFilter``). * Can service the request (``ComputeFilter``). * Satisfy the extra specs associated with the instance type (``ComputeCapabilitiesFilter``). * Satisfy any architecture, hypervisor type, or virtual machine mode properties specified on the instance's image properties (``ImagePropertiesFilter``). * Are on a different host than other instances of a group (if requested) (``ServerGroupAntiAffinityFilter``). * Are in a set of group hosts (if requested) (``ServerGroupAffinityFilter``). The scheduler chooses a new host when an instance is migrated. When evacuating instances from a host, the scheduler service honors the target host defined by the administrator on the :command:`nova evacuate` command. If a target is not defined by the administrator, the scheduler determines the target host. For information about instance evacuation, see :ref:`Evacuate instances `. .. _compute-scheduler-filters: Filter scheduler ~~~~~~~~~~~~~~~~ The filter scheduler (``nova.scheduler.filter_scheduler.FilterScheduler``) is the default scheduler for scheduling virtual machine instances. It supports filtering and weighting to make informed decisions on where a new instance should be created. When the filter scheduler receives a request for a resource, it first applies filters to determine which hosts are eligible for consideration when dispatching a resource. Filters are binary: either a host is accepted by the filter, or it is rejected. Hosts that are accepted by the filter are then processed by a different algorithm to decide which hosts to use for that request, described in the :ref:`weights` section. **Filtering** .. figure:: /figures/filteringWorkflow1.png The ``available_filters`` configuration option in ``nova.conf`` provides the Compute service with the list of the filters that are available for use by the scheduler. The default setting specifies all of the filters that are included with the Compute service: .. code-block:: ini [filter_scheduler] available_filters = nova.scheduler.filters.all_filters This configuration option can be specified multiple times. For example, if you implemented your own custom filter in Python called ``myfilter.MyFilter`` and you wanted to use both the built-in filters and your custom filter, your ``nova.conf`` file would contain: .. code-block:: ini [filter_scheduler] available_filters = nova.scheduler.filters.all_filters available_filters = myfilter.MyFilter The ``enabled_filters`` configuration option in ``nova.conf`` defines the list of filters that are applied by the ``nova-scheduler`` service. The default filters are: .. code-block:: ini [filter_scheduler] enabled_filters = RetryFilter, AvailabilityZoneFilter, ComputeCapabilitiesFilter, ImagePropertiesFilter, ServerGroupAntiAffinityFilter, ServerGroupAffinityFilter Compute filters ~~~~~~~~~~~~~~~ The following sections describe the available compute filters. AggregateCoreFilter ------------------- Filters host by CPU core numbers with a per-aggregate ``cpu_allocation_ratio`` value. If the per-aggregate value is not found, the value falls back to the global setting. If the host is in more than one aggregate and more than one value is found, the minimum value will be used. For information about how to use this filter, see :ref:`host-aggregates`. See also :ref:`CoreFilter`. Note the ``cpu_allocation_ratio`` :ref:`bug 1804125 ` restriction. AggregateDiskFilter ------------------- Filters host by disk allocation with a per-aggregate ``disk_allocation_ratio`` value. If the per-aggregate value is not found, the value falls back to the global setting. If the host is in more than one aggregate and more than one value is found, the minimum value will be used. For information about how to use this filter, see :ref:`host-aggregates`. See also :ref:`DiskFilter`. Note the ``disk_allocation_ratio`` :ref:`bug 1804125 ` restriction. AggregateImagePropertiesIsolation --------------------------------- Matches properties defined in an image's metadata against those of aggregates to determine host matches: * If a host belongs to an aggregate and the aggregate defines one or more metadata that matches an image's properties, that host is a candidate to boot the image's instance. * If a host does not belong to any aggregate, it can boot instances from all images. For example, the following aggregate ``myWinAgg`` has the Windows operating system as metadata (named 'windows'): .. code-block:: console $ openstack aggregate show myWinAgg +-------------------+----------------------------+ | Field | Value | +-------------------+----------------------------+ | availability_zone | zone1 | | created_at | 2017-01-01T15:36:44.000000 | | deleted | False | | deleted_at | None | | hosts | [u'sf-devel'] | | id | 1 | | name | myWinAgg | | properties | os_distro='windows' | | updated_at | None | +-------------------+----------------------------+ In this example, because the following Win-2012 image has the ``windows`` property, it boots on the ``sf-devel`` host (all other filters being equal): .. code-block:: console $ openstack image show Win-2012 +------------------+------------------------------------------------------+ | Field | Value | +------------------+------------------------------------------------------+ | checksum | ee1eca47dc88f4879d8a229cc70a07c6 | | container_format | bare | | created_at | 2016-12-13T09:30:30Z | | disk_format | qcow2 | | ... | | name | Win-2012 | | ... | | properties | os_distro='windows' | | ... | You can configure the ``AggregateImagePropertiesIsolation`` filter by using the following options in the ``nova.conf`` file: .. code-block:: ini # Considers only keys matching the given namespace (string). # Multiple values can be given, as a comma-separated list. aggregate_image_properties_isolation_namespace = # Separator used between the namespace and keys (string). aggregate_image_properties_isolation_separator = . .. _AggregateInstanceExtraSpecsFilter: AggregateInstanceExtraSpecsFilter --------------------------------- Matches properties defined in extra specs for an instance type against admin-defined properties on a host aggregate. Works with specifications that are scoped with ``aggregate_instance_extra_specs``. Multiple values can be given, as a comma-separated list. For backward compatibility, also works with non-scoped specifications; this action is highly discouraged because it conflicts with :ref:`ComputeCapabilitiesFilter` filter when you enable both filters. For information about how to use this filter, see the :ref:`host-aggregates` section. AggregateIoOpsFilter -------------------- Filters host by disk allocation with a per-aggregate ``max_io_ops_per_host`` value. If the per-aggregate value is not found, the value falls back to the global setting. If the host is in more than one aggregate and more than one value is found, the minimum value will be used. For information about how to use this filter, see :ref:`host-aggregates`. See also :ref:`IoOpsFilter`. AggregateMultiTenancyIsolation ------------------------------ Ensures hosts in tenant-isolated :ref:`host-aggregates` will only be available to a specified set of tenants. If a host is in an aggregate that has the ``filter_tenant_id`` metadata key, the host can build instances from only that tenant or comma-separated list of tenants. A host can be in different aggregates. If a host does not belong to an aggregate with the metadata key, the host can build instances from all tenants. This does not restrict the tenant from creating servers on hosts outside the tenant-isolated aggregate. For example, consider there are two available hosts for scheduling, HostA and HostB. HostB is in an aggregate isolated to tenant X. A server create request from tenant X will result in either HostA *or* HostB as candidates during scheduling. A server create request from another tenant Y will result in only HostA being a scheduling candidate since HostA is not part of the tenant-isolated aggregate. .. note:: There is a `known limitation `_ with the number of tenants that can be isolated per aggregate using this filter. This limitation does not exist, however, for the `Tenant Isolation with Placement`_ filtering capability added in the 18.0.0 Rocky release. AggregateNumInstancesFilter --------------------------- Filters host by number of instances with a per-aggregate ``max_instances_per_host`` value. If the per-aggregate value is not found, the value falls back to the global setting. If the host is in more than one aggregate and thus more than one value is found, the minimum value will be used. For information about how to use this filter, see :ref:`host-aggregates`. See also :ref:`NumInstancesFilter`. AggregateRamFilter ------------------ Filters host by RAM allocation of instances with a per-aggregate ``ram_allocation_ratio`` value. If the per-aggregate value is not found, the value falls back to the global setting. If the host is in more than one aggregate and thus more than one value is found, the minimum value will be used. For information about how to use this filter, see :ref:`host-aggregates`. See also :ref:`ramfilter`. Note the ``ram_allocation_ratio`` :ref:`bug 1804125 ` restriction. AggregateTypeAffinityFilter --------------------------- This filter passes hosts if no ``instance_type`` key is set or the ``instance_type`` aggregate metadata value contains the name of the ``instance_type`` requested. The value of the ``instance_type`` metadata entry is a string that may contain either a single ``instance_type`` name or a comma-separated list of ``instance_type`` names, such as ``m1.nano`` or ``m1.nano,m1.small``. For information about how to use this filter, see :ref:`host-aggregates`. AllHostsFilter -------------- This is a no-op filter. It does not eliminate any of the available hosts. AvailabilityZoneFilter ---------------------- Filters hosts by availability zone. You must enable this filter for the scheduler to respect availability zones in requests. .. _ComputeCapabilitiesFilter: ComputeCapabilitiesFilter ------------------------- Matches properties defined in extra specs for an instance type against compute capabilities. If an extra specs key contains a colon (``:``), anything before the colon is treated as a namespace and anything after the colon is treated as the key to be matched. If a namespace is present and is not ``capabilities``, the filter ignores the namespace. For backward compatibility, also treats the extra specs key as the key to be matched if no namespace is present; this action is highly discouraged because it conflicts with :ref:`AggregateInstanceExtraSpecsFilter` filter when you enable both filters. Some virt drivers support reporting CPU traits to the Placement service. With that feature available, you should consider using traits in flavors instead of ComputeCapabilitiesFilter, because traits provide consistent naming for CPU features in some virt drivers and querying traits is efficient. For more detail, please see `Support Matrix `_, :ref:`Required traits `, :ref:`Forbidden traits ` and `Report CPU features to the Placement service `_. Also refer to `Compute capabilities as traits`_. .. _ComputeFilter: ComputeFilter ------------- Passes all hosts that are operational and enabled. In general, you should always enable this filter. .. _CoreFilter: CoreFilter ---------- .. deprecated:: 19.0.0 ``CoreFilter`` is deprecated since the 19.0.0 Stein release. VCPU filtering is performed natively using the Placement service when using the ``filter_scheduler`` driver. Furthermore, enabling CoreFilter may incorrectly filter out `baremetal nodes`_ which must be scheduled using custom resource classes. Only schedules instances on hosts if sufficient CPU cores are available. If this filter is not set, the scheduler might over-provision a host based on cores. For example, the virtual cores running on an instance may exceed the physical cores. You can configure this filter to enable a fixed amount of vCPU overcommitment by using the ``cpu_allocation_ratio`` configuration option in ``nova.conf``. The default setting is: .. code-block:: ini cpu_allocation_ratio = 16.0 With this setting, if 8 vCPUs are on a node, the scheduler allows instances up to 128 vCPU to be run on that node. To disallow vCPU overcommitment set: .. code-block:: ini cpu_allocation_ratio = 1.0 .. note:: The Compute API always returns the actual number of CPU cores available on a compute node regardless of the value of the ``cpu_allocation_ratio`` configuration key. As a result changes to the ``cpu_allocation_ratio`` are not reflected via the command line clients or the dashboard. Changes to this configuration key are only taken into account internally in the scheduler. DifferentHostFilter ------------------- Schedules the instance on a different host from a set of instances. To take advantage of this filter, the requester must pass a scheduler hint, using ``different_host`` as the key and a list of instance UUIDs as the value. This filter is the opposite of the ``SameHostFilter``. Using the :command:`openstack server create` command, use the ``--hint`` flag. For example: .. code-block:: console $ openstack server create --image cedef40a-ed67-4d10-800e-17455edce175 \ --flavor 1 --hint different_host=a0cf03a5-d921-4877-bb5c-86d26cf818e1 \ --hint different_host=8c19174f-4220-44f0-824a-cd1eeef10287 server-1 With the API, use the ``os:scheduler_hints`` key. For example: .. code-block:: json { "server": { "name": "server-1", "imageRef": "cedef40a-ed67-4d10-800e-17455edce175", "flavorRef": "1" }, "os:scheduler_hints": { "different_host": [ "a0cf03a5-d921-4877-bb5c-86d26cf818e1", "8c19174f-4220-44f0-824a-cd1eeef10287" ] } } .. _DiskFilter: DiskFilter ---------- .. deprecated:: 19.0.0 ``DiskFilter`` is deprecated since the 19.0.0 Stein release. DISK_GB filtering is performed natively using the Placement service when using the ``filter_scheduler`` driver. Furthermore, enabling DiskFilter may incorrectly filter out `baremetal nodes`_ which must be scheduled using custom resource classes. Only schedules instances on hosts if there is sufficient disk space available for root and ephemeral storage. You can configure this filter to enable a fixed amount of disk overcommitment by using the ``disk_allocation_ratio`` configuration option in the ``nova.conf`` configuration file. The default setting disables the possibility of the overcommitment and allows launching a VM only if there is a sufficient amount of disk space available on a host: .. code-block:: ini disk_allocation_ratio = 1.0 DiskFilter always considers the value of the ``disk_available_least`` property and not the one of the ``free_disk_gb`` property of a hypervisor's statistics: .. code-block:: console $ openstack hypervisor stats show +----------------------+-------+ | Field | Value | +----------------------+-------+ | count | 1 | | current_workload | 0 | | disk_available_least | 14 | | free_disk_gb | 27 | | free_ram_mb | 15374 | | local_gb | 27 | | local_gb_used | 0 | | memory_mb | 15886 | | memory_mb_used | 512 | | running_vms | 0 | | vcpus | 8 | | vcpus_used | 0 | +----------------------+-------+ As it can be viewed from the command output above, the amount of the available disk space can be less than the amount of the free disk space. It happens because the ``disk_available_least`` property accounts for the virtual size rather than the actual size of images. If you use an image format that is sparse or copy on write so that each virtual instance does not require a 1:1 allocation of a virtual disk to a physical storage, it may be useful to allow the overcommitment of disk space. When disk space is overcommitted, the value of ``disk_available_least`` can be negative. Rather than rounding up to 0, the original negative value is reported, as this way a user can see the amount by which they are overcommitting, and the disk weigher can select a host which is less overcommitted than another host. To enable scheduling instances while overcommitting disk resources on the node, adjust the value of the ``disk_allocation_ratio`` configuration option to greater than ``1.0``: .. code-block:: none disk_allocation_ratio > 1.0 .. note:: If the value is set to ``>1``, we recommend keeping track of the free disk space, as the value approaching ``0`` may result in the incorrect functioning of instances using it at the moment. .. _ImagePropertiesFilter: ImagePropertiesFilter --------------------- Filters hosts based on properties defined on the instance's image. It passes hosts that can support the specified image properties contained in the instance. Properties include the architecture, hypervisor type, hypervisor version (for Xen hypervisor type only), and virtual machine mode. For example, an instance might require a host that runs an ARM-based processor, and QEMU as the hypervisor. You can decorate an image with these properties by using: .. code-block:: console $ openstack image set --architecture arm --property hypervisor_type=qemu \ img-uuid The image properties that the filter checks for are: ``architecture`` describes the machine architecture required by the image. Examples are ``i686``, ``x86_64``, ``arm``, and ``ppc64``. ``hypervisor_type`` describes the hypervisor required by the image. Examples are ``xen``, ``qemu``, and ``xenapi``. .. note:: ``qemu`` is used for both QEMU and KVM hypervisor types. ``hypervisor_version_requires`` describes the hypervisor version required by the image. The property is supported for Xen hypervisor type only. It can be used to enable support for multiple hypervisor versions, and to prevent instances with newer Xen tools from being provisioned on an older version of a hypervisor. If available, the property value is compared to the hypervisor version of the compute host. To filter the hosts by the hypervisor version, add the ``hypervisor_version_requires`` property on the image as metadata and pass an operator and a required hypervisor version as its value: .. code-block:: console $ openstack image set --property hypervisor_type=xen --property \ hypervisor_version_requires=">=4.3" img-uuid ``vm_mode`` describes the hypervisor application binary interface (ABI) required by the image. Examples are ``xen`` for Xen 3.0 paravirtual ABI, ``hvm`` for native ABI, ``uml`` for User Mode Linux paravirtual ABI, ``exe`` for container virt executable ABI. IsolatedHostsFilter ------------------- Allows the admin to define a special (isolated) set of images and a special (isolated) set of hosts, such that the isolated images can only run on the isolated hosts, and the isolated hosts can only run isolated images. The flag ``restrict_isolated_hosts_to_isolated_images`` can be used to force isolated hosts to only run isolated images. The logic within the filter depends on the ``restrict_isolated_hosts_to_isolated_images`` config option, which defaults to True. When True, a volume-backed instance will not be put on an isolated host. When False, a volume-backed instance can go on any host, isolated or not. The admin must specify the isolated set of images and hosts in the ``nova.conf`` file using the ``isolated_hosts`` and ``isolated_images`` configuration options. For example: .. code-block:: ini [filter_scheduler] isolated_hosts = server1, server2 isolated_images = 342b492c-128f-4a42-8d3a-c5088cf27d13, ebd267a6-ca86-4d6c-9a0e-bd132d6b7d09 .. _IoOpsFilter: IoOpsFilter ----------- The IoOpsFilter filters hosts by concurrent I/O operations on it. Hosts with too many concurrent I/O operations will be filtered out. The ``max_io_ops_per_host`` option specifies the maximum number of I/O intensive instances allowed to run on a host. A host will be ignored by the scheduler if more than ``max_io_ops_per_host`` instances in build, resize, snapshot, migrate, rescue or unshelve task states are running on it. JsonFilter ---------- .. warning:: This filter is not enabled by default and not comprehensively tested, and thus could fail to work as expected in non-obvious ways. Furthermore, the filter variables are based on attributes of the `HostState`_ class which could change from release to release so usage of this filter is generally not recommended. Consider using other filters such as the :ref:`ImagePropertiesFilter` or :ref:`traits-based scheduling `. The JsonFilter allows a user to construct a custom filter by passing a scheduler hint in JSON format. The following operators are supported: * = * < * > * in * <= * >= * not * or * and The filter supports any attribute in the `HostState`_ class such as the following variables: * ``$free_ram_mb`` * ``$free_disk_mb`` * ``$hypervisor_hostname`` * ``$total_usable_ram_mb`` * ``$vcpus_total`` * ``$vcpus_used`` Using the :command:`openstack server create` command, use the ``--hint`` flag: .. code-block:: console $ openstack server create --image 827d564a-e636-4fc4-a376-d36f7ebe1747 \ --flavor 1 --hint query='[">=","$free_ram_mb",1024]' server1 With the API, use the ``os:scheduler_hints`` key: .. code-block:: json { "server": { "name": "server-1", "imageRef": "cedef40a-ed67-4d10-800e-17455edce175", "flavorRef": "1" }, "os:scheduler_hints": { "query": "[\">=\",\"$free_ram_mb\",1024]" } } .. _HostState: https://opendev.org/openstack/nova/src/branch/master/nova/scheduler/host_manager.py MetricsFilter ------------- Filters hosts based on meters ``weight_setting``. Only hosts with the available meters are passed so that the metrics weigher will not fail due to these hosts. NUMATopologyFilter ------------------ Filters hosts based on the NUMA topology that was specified for the instance through the use of flavor ``extra_specs`` in combination with the image properties, as described in detail in the `related nova-spec document `_. Filter will try to match the exact NUMA cells of the instance to those of the host. It will consider the standard over-subscription limits for each host NUMA cell, and provide limits to the compute host accordingly. .. note:: If instance has no topology defined, it will be considered for any host. If instance has a topology defined, it will be considered only for NUMA capable hosts. .. _NumInstancesFilter: NumInstancesFilter ------------------ Hosts that have more instances running than specified by the ``max_instances_per_host`` option are filtered out when this filter is in place. PciPassthroughFilter -------------------- The filter schedules instances on a host if the host has devices that meet the device requests in the ``extra_specs`` attribute for the flavor. .. _RamFilter: RamFilter --------- .. deprecated:: 19.0.0 ``RamFilter`` is deprecated since the 19.0.0 Stein release. MEMORY_MB filtering is performed natively using the Placement service when using the ``filter_scheduler`` driver. Furthermore, enabling RamFilter may incorrectly filter out `baremetal nodes`_ which must be scheduled using custom resource classes. .. _baremetal nodes: https://docs.openstack.org/ironic/latest/install/configure-nova-flavors.html Only schedules instances on hosts that have sufficient RAM available. If this filter is not set, the scheduler may over provision a host based on RAM (for example, the RAM allocated by virtual machine instances may exceed the physical RAM). You can configure this filter to enable a fixed amount of RAM overcommitment by using the ``ram_allocation_ratio`` configuration option in ``nova.conf``. The default setting is: .. code-block:: ini ram_allocation_ratio = 1.5 This setting enables 1.5 GB instances to run on any compute node with 1 GB of free RAM. RetryFilter ----------- Filters out hosts that have already been attempted for scheduling purposes. If the scheduler selects a host to respond to a service request, and the host fails to respond to the request, this filter prevents the scheduler from retrying that host for the service request. This filter is only useful if the ``scheduler_max_attempts`` configuration option is set to a value greater than zero. SameHostFilter -------------- Schedules the instance on the same host as another instance in a set of instances. To take advantage of this filter, the requester must pass a scheduler hint, using ``same_host`` as the key and a list of instance UUIDs as the value. This filter is the opposite of the ``DifferentHostFilter``. Using the :command:`openstack server create` command, use the ``--hint`` flag: .. code-block:: console $ openstack server create --image cedef40a-ed67-4d10-800e-17455edce175 \ --flavor 1 --hint same_host=a0cf03a5-d921-4877-bb5c-86d26cf818e1 \ --hint same_host=8c19174f-4220-44f0-824a-cd1eeef10287 server-1 With the API, use the ``os:scheduler_hints`` key: .. code-block:: json { "server": { "name": "server-1", "imageRef": "cedef40a-ed67-4d10-800e-17455edce175", "flavorRef": "1" }, "os:scheduler_hints": { "same_host": [ "a0cf03a5-d921-4877-bb5c-86d26cf818e1", "8c19174f-4220-44f0-824a-cd1eeef10287" ] } } .. _ServerGroupAffinityFilter: ServerGroupAffinityFilter ------------------------- The ServerGroupAffinityFilter ensures that an instance is scheduled on to a host from a set of group hosts. To take advantage of this filter, the requester must create a server group with an ``affinity`` policy, and pass a scheduler hint, using ``group`` as the key and the server group UUID as the value. Using the :command:`openstack server create` command, use the ``--hint`` flag. For example: .. code-block:: console $ openstack server group create --policy affinity group-1 $ openstack server create --image IMAGE_ID --flavor 1 \ --hint group=SERVER_GROUP_UUID server-1 .. _ServerGroupAntiAffinityFilter: ServerGroupAntiAffinityFilter ----------------------------- The ServerGroupAntiAffinityFilter ensures that each instance in a group is on a different host. To take advantage of this filter, the requester must create a server group with an ``anti-affinity`` policy, and pass a scheduler hint, using ``group`` as the key and the server group UUID as the value. Using the :command:`openstack server create` command, use the ``--hint`` flag. For example: .. code-block:: console $ openstack server group create --policy anti-affinity group-1 $ openstack server create --image IMAGE_ID --flavor 1 \ --hint group=SERVER_GROUP_UUID server-1 SimpleCIDRAffinityFilter ------------------------ Schedules the instance based on host IP subnet range. To take advantage of this filter, the requester must specify a range of valid IP address in CIDR format, by passing two scheduler hints: ``build_near_host_ip`` The first IP address in the subnet (for example, ``192.168.1.1``) ``cidr`` The CIDR that corresponds to the subnet (for example, ``/24``) Using the :command:`openstack server create` command, use the ``--hint`` flag. For example, to specify the IP subnet ``192.168.1.1/24``: .. code-block:: console $ openstack server create --image cedef40a-ed67-4d10-800e-17455edce175 \ --flavor 1 --hint build_near_host_ip=192.168.1.1 --hint cidr=/24 server-1 With the API, use the ``os:scheduler_hints`` key: .. code-block:: json { "server": { "name": "server-1", "imageRef": "cedef40a-ed67-4d10-800e-17455edce175", "flavorRef": "1" }, "os:scheduler_hints": { "build_near_host_ip": "192.168.1.1", "cidr": "24" } } .. _weights: Weights ~~~~~~~ When resourcing instances, the filter scheduler filters and weights each host in the list of acceptable hosts. Each time the scheduler selects a host, it virtually consumes resources on it, and subsequent selections are adjusted accordingly. This process is useful when the customer asks for the same large amount of instances, because weight is computed for each requested instance. All weights are normalized before being summed up; the host with the largest weight is given the highest priority. **Weighting hosts** .. figure:: /figures/nova-weighting-hosts.png Hosts are weighted based on the following options in the ``/etc/nova/nova.conf`` file: .. list-table:: Host weighting options :header-rows: 1 :widths: 10, 25, 60 * - Section - Option - Description * - [DEFAULT] - ``ram_weight_multiplier`` - By default, the scheduler spreads instances across all hosts evenly. Set the ``ram_weight_multiplier`` option to a negative number if you prefer stacking instead of spreading. Use a floating-point value. If the per aggregate ``ram_weight_multiplier`` metadata is set, this multiplier will override the configuration option value. * - [DEFAULT] - ``disk_weight_multiplier`` - By default, the scheduler spreads instances across all hosts evenly. Set the ``disk_weight_multiplier`` option to a negative number if you prefer stacking instead of spreading. Use a floating-point value. If the per aggregate ``disk_weight_multiplier`` metadata is set, this multiplier will override the configuration option value. * - [DEFAULT] - ``cpu_weight_multiplier`` - By default, the scheduler spreads instances across all hosts evenly. Set the ``cpu_weight_multiplier`` option to a negative number if you prefer stacking instead of spreading. Use a floating-point value. If the per aggregate ``cpu_weight_multiplier`` metadata is set, this multiplier will override the configuration option value. * - [DEFAULT] - ``scheduler_host_subset_size`` - New instances are scheduled on a host that is chosen randomly from a subset of the N best hosts. This property defines the subset size from which a host is chosen. A value of 1 chooses the first host returned by the weighting functions. This value must be at least 1. A value less than 1 is ignored, and 1 is used instead. Use an integer value. * - [DEFAULT] - ``scheduler_weight_classes`` - Defaults to ``nova.scheduler.weights.all_weighers``. Hosts are then weighted and sorted with the largest weight winning. * - [DEFAULT] - ``io_ops_weight_multiplier`` - Multiplier used for weighing host I/O operations. A negative value means a preference to choose light workload compute hosts. If the per aggregate ``io_ops_weight_multiplier`` metadata is set, this multiplier will override the configuration option value. * - [filter_scheduler] - ``soft_affinity_weight_multiplier`` - Multiplier used for weighing hosts for group soft-affinity. Only a positive value is allowed. * - [filter_scheduler] If the per aggregate ``soft_affinity_weight_multiplier`` metadata is set, this multiplier will override the configuration option value. - ``soft_anti_affinity_weight_multiplier`` - Multiplier used for weighing hosts for group soft-anti-affinity. Only a positive value is allowed. If the per aggregate ``soft_anti_affinity_weight_multiplier`` metadata is set, this multiplier will override the configuration option value. * - [filter_scheduler] - ``build_failure_weight_multiplier`` - Multiplier used for weighing hosts which have recent build failures. A positive value increases the significance of build failures reported by the host recently, making them less likely to be chosen. If the per aggregate ``build_failure_weight_multiplier`` metadata is set, this multiplier will override the configuration option value. * - [metrics] - ``weight_multiplier`` - Multiplier for weighting meters. Use a floating-point value. If the per aggregate ``metrics_weight_multiplier`` metadata is set, this multiplier will override the configuration option value. * - [metrics] - ``weight_setting`` - Determines how meters are weighted. Use a comma-separated list of metricName=ratio. For example: ``name1=1.0, name2=-1.0`` results in: ``name1.value * 1.0 + name2.value * -1.0`` * - [metrics] - ``required`` - Specifies how to treat unavailable meters: * True - Raises an exception. To avoid the raised exception, you should use the scheduler filter ``MetricFilter`` to filter out hosts with unavailable meters. * False - Treated as a negative factor in the weighting process (uses the ``weight_of_unavailable`` option). * - [metrics] - ``weight_of_unavailable`` - If ``required`` is set to False, and any one of the meters set by ``weight_setting`` is unavailable, the ``weight_of_unavailable`` value is returned to the scheduler. For example: .. code-block:: ini [DEFAULT] scheduler_host_subset_size = 1 scheduler_weight_classes = nova.scheduler.weights.all_weighers ram_weight_multiplier = 1.0 io_ops_weight_multiplier = 2.0 soft_affinity_weight_multiplier = 1.0 soft_anti_affinity_weight_multiplier = 1.0 [metrics] weight_multiplier = 1.0 weight_setting = name1=1.0, name2=-1.0 required = false weight_of_unavailable = -10000.0 Utilization aware scheduling ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ It is possible to schedule VMs using advanced scheduling decisions. These decisions are made based on enhanced usage statistics encompassing data like memory cache utilization, memory bandwidth utilization, or network bandwidth utilization. This is disabled by default. The administrator can configure how the metrics are weighted in the configuration file by using the ``weight_setting`` configuration option in the ``nova.conf`` configuration file. For example to configure metric1 with ratio1 and metric2 with ratio2: .. code-block:: ini weight_setting = "metric1=ratio1, metric2=ratio2" .. _host-aggregates: Host aggregates and availability zones ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Host aggregates are a mechanism for partitioning hosts in an OpenStack cloud, or a region of an OpenStack cloud, based on arbitrary characteristics. Examples where an administrator may want to do this include where a group of hosts have additional hardware or performance characteristics. Host aggregates are not explicitly exposed to users. Instead administrators map flavors to host aggregates. Administrators do this by setting metadata on a host aggregate, and matching flavor extra specifications. The scheduler then endeavors to match user requests for instance of the given flavor to a host aggregate with the same key-value pair in its metadata. Compute nodes can be in more than one host aggregate. Weight multipliers can be controlled on a per-aggregate basis by setting the desired ``xxx_weight_multiplier`` aggregate metadata. Administrators are able to optionally expose a host aggregate as an availability zone. Availability zones are different from host aggregates in that they are explicitly exposed to the user, and hosts can only be in a single availability zone. Administrators can configure a default availability zone where instances will be scheduled when the user fails to specify one. Command-line interface ---------------------- The :command:`nova` command-line client supports the following aggregate-related commands. nova aggregate-list Print a list of all aggregates. nova aggregate-create [] Create a new aggregate named ````, and optionally in availability zone ``[]`` if specified. The command returns the ID of the newly created aggregate. Hosts can be made available to multiple host aggregates. Be careful when adding a host to an additional host aggregate when the host is also in an availability zone. Pay attention when using the :command:`nova aggregate-set-metadata` and :command:`nova aggregate-update` commands to avoid user confusion when they boot instances in different availability zones. An error occurs if you cannot add a particular host to an aggregate zone for which it is not intended. nova aggregate-delete Delete an aggregate with its ```` or ````. nova aggregate-show Show details of the aggregate with its ```` or ````. nova aggregate-add-host Add host with name ```` to aggregate with its ```` or ````. nova aggregate-remove-host Remove the host with name ```` from the aggregate with its ```` or ````. nova aggregate-set-metadata [ ...] Add or update metadata (key-value pairs) associated with the aggregate with its ```` or ````. nova aggregate-update [--name ] [--availability-zone ] Update the name and/or availability zone for the aggregate. nova host-list List all hosts by service. It has been deprecated since microversion 2.43. Use :command:`nova hypervisor-list` instead. nova hypervisor-list [--matching ] [--marker ] [--limit ] List hypervisors. nova host-update [--status ] [--maintenance ] Put/resume host into/from maintenance. It has been deprecated since microversion 2.43. To enable or disable a service, use :command:`nova service-enable` or :command:`nova service-disable` instead. nova service-enable Enable the service. nova service-disable [--reason ] Disable the service. .. note:: Only administrators can access these commands. If you try to use these commands and the user name and tenant that you use to access the Compute service do not have the ``admin`` role or the appropriate privileges, these errors occur: .. code-block:: console ERROR: Policy doesn't allow compute_extension:aggregates to be performed. (HTTP 403) (Request-ID: req-299fbff6-6729-4cef-93b2-e7e1f96b4864) .. code-block:: console ERROR: Policy doesn't allow compute_extension:hosts to be performed. (HTTP 403) (Request-ID: req-ef2400f6-6776-4ea3-b6f1-7704085c27d1) .. _config-sch-for-aggs: Configure scheduler to support host aggregates ---------------------------------------------- One common use case for host aggregates is when you want to support scheduling instances to a subset of compute hosts because they have a specific capability. For example, you may want to allow users to request compute hosts that have SSD drives if they need access to faster disk I/O, or access to compute hosts that have GPU cards to take advantage of GPU-accelerated code. To configure the scheduler to support host aggregates, the :oslo.config:option:`filter_scheduler.enabled_filters` configuration option must contain the ``AggregateInstanceExtraSpecsFilter`` in addition to the other filters used by the scheduler. Add the following line to ``/etc/nova/nova.conf`` on the host that runs the ``nova-scheduler`` service to enable host aggregates filtering, as well as the other filters that are typically enabled: .. code-block:: ini [filter_scheduler] enabled_filters=AggregateInstanceExtraSpecsFilter,RetryFilter,AvailabilityZoneFilter,ComputeCapabilitiesFilter,ImagePropertiesFilter,ServerGroupAntiAffinityFilter,ServerGroupAffinityFilter Example: Specify compute hosts with SSDs ---------------------------------------- This example configures the Compute service to enable users to request nodes that have solid-state drives (SSDs). You create a ``fast-io`` host aggregate in the ``nova`` availability zone and you add the ``ssd=true`` key-value pair to the aggregate. Then, you add the ``node1``, and ``node2`` compute nodes to it. .. code-block:: console $ openstack aggregate create --zone nova fast-io +-------------------+----------------------------+ | Field | Value | +-------------------+----------------------------+ | availability_zone | nova | | created_at | 2016-12-22T07:31:13.013466 | | deleted | False | | deleted_at | None | | id | 1 | | name | fast-io | | updated_at | None | +-------------------+----------------------------+ $ openstack aggregate set --property ssd=true 1 +-------------------+----------------------------+ | Field | Value | +-------------------+----------------------------+ | availability_zone | nova | | created_at | 2016-12-22T07:31:13.000000 | | deleted | False | | deleted_at | None | | hosts | [] | | id | 1 | | name | fast-io | | properties | ssd='true' | | updated_at | None | +-------------------+----------------------------+ $ openstack aggregate add host 1 node1 +-------------------+--------------------------------------------------+ | Field | Value | +-------------------+--------------------------------------------------+ | availability_zone | nova | | created_at | 2016-12-22T07:31:13.000000 | | deleted | False | | deleted_at | None | | hosts | [u'node1'] | | id | 1 | | metadata | {u'ssd': u'true', u'availability_zone': u'nova'} | | name | fast-io | | updated_at | None | +-------------------+--------------------------------------------------+ $ openstack aggregate add host 1 node2 +-------------------+--------------------------------------------------+ | Field | Value | +-------------------+--------------------------------------------------+ | availability_zone | nova | | created_at | 2016-12-22T07:31:13.000000 | | deleted | False | | deleted_at | None | | hosts | [u'node1', u'node2'] | | id | 1 | | metadata | {u'ssd': u'true', u'availability_zone': u'nova'} | | name | fast-io | | updated_at | None | +-------------------+--------------------------------------------------+ Use the :command:`openstack flavor create` command to create the ``ssd.large`` flavor called with an ID of 6, 8 GB of RAM, 80 GB root disk, and 4 vCPUs. .. code-block:: console $ openstack flavor create --id 6 --ram 8192 --disk 80 --vcpus 4 ssd.large +----------------------------+-----------+ | Field | Value | +----------------------------+-----------+ | OS-FLV-DISABLED:disabled | False | | OS-FLV-EXT-DATA:ephemeral | 0 | | disk | 80 | | id | 6 | | name | ssd.large | | os-flavor-access:is_public | True | | ram | 8192 | | rxtx_factor | 1.0 | | swap | | | vcpus | 4 | +----------------------------+-----------+ Once the flavor is created, specify one or more key-value pairs that match the key-value pairs on the host aggregates with scope ``aggregate_instance_extra_specs``. In this case, that is the ``aggregate_instance_extra_specs:ssd=true`` key-value pair. Setting a key-value pair on a flavor is done using the :command:`openstack flavor set` command. .. code-block:: console $ openstack flavor set --property aggregate_instance_extra_specs:ssd=true ssd.large Once it is set, you should see the ``extra_specs`` property of the ``ssd.large`` flavor populated with a key of ``ssd`` and a corresponding value of ``true``. .. code-block:: console $ openstack flavor show ssd.large +----------------------------+-------------------------------------------+ | Field | Value | +----------------------------+-------------------------------------------+ | OS-FLV-DISABLED:disabled | False | | OS-FLV-EXT-DATA:ephemeral | 0 | | disk | 80 | | id | 6 | | name | ssd.large | | os-flavor-access:is_public | True | | properties | aggregate_instance_extra_specs:ssd='true' | | ram | 8192 | | rxtx_factor | 1.0 | | swap | | | vcpus | 4 | +----------------------------+-------------------------------------------+ Now, when a user requests an instance with the ``ssd.large`` flavor, the scheduler only considers hosts with the ``ssd=true`` key-value pair. In this example, these are ``node1`` and ``node2``. Aggregates in Placement ----------------------- Aggregates also exist in placement and are not the same thing as host aggregates in nova. These aggregates are defined (purely) as groupings of related resource providers. Since compute nodes in nova are represented in placement as resource providers, they can be added to a placement aggregate as well. For example, get the uuid of the compute node using :command:`openstack hypervisor list` and add it to an aggregate in placement using :command:`openstack resource provider aggregate set`. .. code-block:: console $ openstack --os-compute-api-version=2.53 hypervisor list +--------------------------------------+---------------------+-----------------+-----------------+-------+ | ID | Hypervisor Hostname | Hypervisor Type | Host IP | State | +--------------------------------------+---------------------+-----------------+-----------------+-------+ | 815a5634-86fb-4e1e-8824-8a631fee3e06 | node1 | QEMU | 192.168.1.123 | up | +--------------------------------------+---------------------+-----------------+-----------------+-------+ $ openstack --os-placement-api-version=1.2 resource provider aggregate set --aggregate df4c74f3-d2c4-4991-b461-f1a678e1d161 815a5634-86fb-4e1e-8824-8a631fee3e06 Some scheduling filter operations can be performed by placement for increased speed and efficiency. .. note:: The nova-api service attempts (as of nova 18.0.0) to automatically mirror the association of a compute host with an aggregate when an administrator adds or removes a host to/from a nova host aggregate. This should alleviate the need to manually create those association records in the placement API using the ``openstack resource provider aggregate set`` CLI invocation. Tenant Isolation with Placement ------------------------------- In order to use placement to isolate tenants, there must be placement aggregates that match the membership and UUID of nova host aggregates that you want to use for isolation. The same key pattern in aggregate metadata used by the `AggregateMultiTenancyIsolation`_ filter controls this function, and is enabled by setting `[scheduler]/limit_tenants_to_placement_aggregate=True`. .. code-block:: console $ openstack --os-compute-api-version=2.53 aggregate create myagg +-------------------+--------------------------------------+ | Field | Value | +-------------------+--------------------------------------+ | availability_zone | None | | created_at | 2018-03-29T16:22:23.175884 | | deleted | False | | deleted_at | None | | id | 4 | | name | myagg | | updated_at | None | | uuid | 019e2189-31b3-49e1-aff2-b220ebd91c24 | +-------------------+--------------------------------------+ $ openstack --os-compute-api-version=2.53 aggregate add host myagg node1 +-------------------+--------------------------------------+ | Field | Value | +-------------------+--------------------------------------+ | availability_zone | None | | created_at | 2018-03-29T16:22:23.175884 | | deleted | False | | deleted_at | None | | hosts | [u'node1'] | | id | 4 | | name | myagg | | updated_at | None | | uuid | 019e2189-31b3-49e1-aff2-b220ebd91c24 | +-------------------+--------------------------------------+ $ openstack project list -f value | grep 'demo' 9691591f913949818a514f95286a6b90 demo $ openstack aggregate set --property filter_tenant_id=9691591f913949818a514f95286a6b90 myagg $ openstack --os-placement-api-version=1.2 resource provider aggregate set --aggregate 019e2189-31b3-49e1-aff2-b220ebd91c24 815a5634-86fb-4e1e-8824-8a631fee3e06 Note that the ``filter_tenant_id`` metadata key can be optionally suffixed with any string for multiple tenants, such as ``filter_tenant_id3=$tenantid``. Availability Zones with Placement --------------------------------- In order to use placement to honor availability zone requests, there must be placement aggregates that match the membership and UUID of nova host aggregates that you assign as availability zones. The same key in aggregate metadata used by the `AvailabilityZoneFilter` filter controls this function, and is enabled by setting `[scheduler]/query_placement_for_availability_zone=True`. .. code-block:: console $ openstack --os-compute-api-version=2.53 aggregate create myaz +-------------------+--------------------------------------+ | Field | Value | +-------------------+--------------------------------------+ | availability_zone | None | | created_at | 2018-03-29T16:22:23.175884 | | deleted | False | | deleted_at | None | | id | 4 | | name | myaz | | updated_at | None | | uuid | 019e2189-31b3-49e1-aff2-b220ebd91c24 | +-------------------+--------------------------------------+ $ openstack --os-compute-api-version=2.53 aggregate add host myaz node1 +-------------------+--------------------------------------+ | Field | Value | +-------------------+--------------------------------------+ | availability_zone | None | | created_at | 2018-03-29T16:22:23.175884 | | deleted | False | | deleted_at | None | | hosts | [u'node1'] | | id | 4 | | name | myagg | | updated_at | None | | uuid | 019e2189-31b3-49e1-aff2-b220ebd91c24 | +-------------------+--------------------------------------+ $ openstack aggregate set --property availability_zone=az002 myaz $ openstack --os-placement-api-version=1.2 resource provider aggregate set --aggregate 019e2189-31b3-49e1-aff2-b220ebd91c24 815a5634-86fb-4e1e-8824-8a631fee3e06 With the above configuration, the `AvailabilityZoneFilter` filter can be disabled in `[filter_scheduler]/enabled_filters` while retaining proper behavior (and doing so with the higher performance of placement's implementation). XenServer hypervisor pools to support live migration ---------------------------------------------------- When using the XenAPI-based hypervisor, the Compute service uses host aggregates to manage XenServer Resource pools, which are used in supporting live migration. Allocation ratios ~~~~~~~~~~~~~~~~~ The following configuration options exist to control allocation ratios per compute node to support over-commit of resources: * :oslo.config:option:`cpu_allocation_ratio`: allows overriding the VCPU inventory allocation ratio for a compute node * :oslo.config:option:`ram_allocation_ratio`: allows overriding the MEMORY_MB inventory allocation ratio for a compute node * :oslo.config:option:`disk_allocation_ratio`: allows overriding the DISK_GB inventory allocation ratio for a compute node Prior to the 19.0.0 Stein release, if left unset, the ``cpu_allocation_ratio`` defaults to 16.0, the ``ram_allocation_ratio`` defaults to 1.5, and the ``disk_allocation_ratio`` defaults to 1.0. Starting with the 19.0.0 Stein release, the following configuration options control the initial allocation ratio values for a compute node: * :oslo.config:option:`initial_cpu_allocation_ratio`: the initial VCPU inventory allocation ratio for a new compute node record, defaults to 16.0 * :oslo.config:option:`initial_ram_allocation_ratio`: the initial MEMORY_MB inventory allocation ratio for a new compute node record, defaults to 1.5 * :oslo.config:option:`initial_disk_allocation_ratio`: the initial DISK_GB inventory allocation ratio for a new compute node record, defaults to 1.0 Scheduling considerations ------------------------- The allocation ratio configuration is used both during reporting of compute node `resource provider inventory`_ to the placement service and during scheduling. The (deprecated) `CoreFilter`_, `DiskFilter`_ and `RamFilter`_ filters will use the allocation ratio from the compute node directly when calculating available capacity on a given node during scheduling. The `AggregateCoreFilter`_, `AggregateDiskFilter`_ and `AggregateRamFilter`_ filters allow overriding per-compute allocation ratios by setting an allocation ratio value using host aggregate metadata. This provides a convenient way to manage a group of compute hosts with similar allocation ratios while leaving the configuration settings alone. .. _bug-1804125: .. note:: Regarding the `AggregateCoreFilter`_, `AggregateDiskFilter`_ and `AggregateRamFilter`_, starting in 15.0.0 (Ocata) there is a behavior change where aggregate-based overcommit ratios will no longer be honored during scheduling for the FilterScheduler. Instead, overcommit values must be set on a per-compute-node basis in the Nova configuration files. If you have been relying on per-aggregate overcommit, during your upgrade, you must change to using per-compute-node overcommit ratios in order for your scheduling behavior to stay consistent. Otherwise, you may notice increased NoValidHost scheduling failures as the aggregate-based overcommit is no longer being considered. See `bug 1804125 `_ for more details. .. _resource provider inventory: https://developer.openstack.org/api-ref/placement/?expanded=#resource-provider-inventories Usage scenarios --------------- Since allocation ratios can be set via nova configuration, host aggregate metadata and the placement API, it can be confusing to know which should be used. This really depends on your scenario. A few common scenarios are detailed here. 1. When the deployer wants to **always** set an override value for a resource on a compute node, the deployer would ensure that the ``[DEFAULT]/cpu_allocation_ratio``, ``[DEFAULT]/ram_allocation_ratio`` and ``[DEFAULT]/disk_allocation_ratio`` configuration options are set to a non-None value (or greater than 0.0 before the 19.0.0 Stein release). This will make the ``nova-compute`` service overwrite any externally-set allocation ratio values set via the placement REST API. 2. When the deployer wants to set an **initial** value for a compute node allocation ratio but wants to allow an admin to adjust this afterwards without making any configuration file changes, the deployer would set the ``[DEFAULT]/initial_cpu_allocation_ratio``, ``[DEFAULT]/initial_ram_allocation_ratio`` and ``[DEFAULT]/initial_disk_allocation_ratio`` configuration options and then manage the allocation ratios using the placement REST API (or `osc-placement`_ command line interface). For example: .. code-block:: console $ openstack resource provider inventory set --resource VCPU:allocation_ratio=1.0 815a5634-86fb-4e1e-8824-8a631fee3e06 Note the :ref:`bug 1804125 ` restriction. 3. When the deployer wants to **always** use the placement API to set allocation ratios, then the deployer should ensure that ``[DEFAULT]/xxx_allocation_ratio`` options are all set to None (the default since 19.0.0 Stein, 0.0 before Stein) and then manage the allocation ratios using the placement REST API (or `osc-placement`_ command line interface). This scenario is the workaround for `bug 1804125 `_. .. _osc-placement: https://docs.openstack.org/osc-placement/latest/index.html Cells considerations ~~~~~~~~~~~~~~~~~~~~ By default cells are enabled for scheduling new instances but they can be disabled (new schedulings to the cell are blocked). This may be useful for users while performing cell maintenance, failures or other interventions. It is to be noted that creating pre-disabled cells and enabling/disabling existing cells should either be followed by a restart or SIGHUP of the nova-scheduler service for the changes to take effect. Command-line interface ---------------------- The :command:`nova-manage` command-line client supports the cell-disable related commands. To enable or disable a cell, use :command:`nova-manage cell_v2 update_cell` and to create pre-disabled cells, use :command:`nova-manage cell_v2 create_cell`. See the :ref:`man-page-cells-v2` man page for details on command usage. Compute capabilities as traits ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Starting with the 19.0.0 Stein release, the ``nova-compute`` service will report certain ``COMPUTE_*`` traits based on its compute driver capabilities to the placement service. The traits will be associated with the resource provider for that compute service. These traits can be used during scheduling by configuring flavors with :ref:`Required traits ` or :ref:`Forbidden traits `. For example, if you have a host aggregate with a set of compute nodes that support multi-attach volumes, you can restrict a flavor to that aggregate by adding the ``trait:COMPUTE_VOLUME_MULTI_ATTACH=required`` extra spec to the flavor and then restrict the flavor to the aggregate :ref:`as normal `. Here is an example of a libvirt compute node resource provider that is exposing some CPU features as traits, driver capabilities as traits, and a custom trait denoted by the ``CUSTOM_`` prefix: .. code-block:: console $ openstack --os-placement-api-version 1.6 resource provider trait list \ > d9b3dbc4-50e2-42dd-be98-522f6edaab3f --sort-column name +---------------------------------------+ | name | +---------------------------------------+ | COMPUTE_DEVICE_TAGGING | | COMPUTE_NET_ATTACH_INTERFACE | | COMPUTE_NET_ATTACH_INTERFACE_WITH_TAG | | COMPUTE_TRUSTED_CERTS | | COMPUTE_VOLUME_ATTACH_WITH_TAG | | COMPUTE_VOLUME_EXTEND | | COMPUTE_VOLUME_MULTI_ATTACH | | CUSTOM_IMAGE_TYPE_RBD | | HW_CPU_X86_MMX | | HW_CPU_X86_SSE | | HW_CPU_X86_SSE2 | | HW_CPU_X86_SVM | +---------------------------------------+ **Rules** There are some rules associated with capability-defined traits. 1. The compute service "owns" these traits and will add/remove them when the ``nova-compute`` service starts and when the ``update_available_resource`` periodic task runs, with run intervals controlled by config option :oslo.config:option:`update_resources_interval`. 2. The compute service will not remove any custom traits set on the resource provider externally, such as the ``CUSTOM_IMAGE_TYPE_RBD`` trait in the example above. 3. If compute-owned traits are removed from the resource provider externally, for example by running ``openstack resource provider trait delete ``, the compute service will add its traits again on restart or SIGHUP. 4. If a compute trait is set on the resource provider externally which is not supported by the driver, for example by adding the ``COMPUTE_VOLUME_EXTEND`` trait when the driver does not support that capability, the compute service will automatically remove the unsupported trait on restart or SIGHUP. 5. Compute capability traits are standard traits defined in the `os-traits`_ library. .. _os-traits: https://opendev.org/openstack/os-traits/src/branch/master/os_traits/compute