Filters

Matches properties defined in an instance type's extra specs against admin-defined properties on a host aggregate. See the host aggregates section for documentation on how to use this filter.

Isolates tenants to specifichost aggregates. If a host is in an aggregate that has the metadata key filter_tenant_id it will only create instances from that tenant (or list of tenants). A host can be in different aggregates. If a host does not belong to an aggregate with the metadata key, it can create instances from all tenants.

This is a no-op filter, it does not eliminate any of the available hosts.

Filters hosts by availability zone. This filter must be enabled for the scheduler to respect availability zones in requests.

Matches properties defined in an instance type's extra specs 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', it is ignored by this filter.

	Note
	Disable the ComputeCapabilitiesFilter when using a Bare Metal configuration, due to bug 1129485

Filters hosts by flavor (also known as instance type) and image properties. The scheduler will check to ensure that a compute host has sufficient capabilities to run a virtual machine instance that corresponds to the specified flavor. If the image has properties specified, this filter will also check that the host can support them. The image properties that the filter checks for are:

In general, this filter should always be enabled.

Only schedule instances on hosts if there are sufficient CPU cores available. If this filter is not set, the scheduler may over provision a host based on cores (i.e., the virtual cores running on an instance may exceed the physical cores).

This filter can be configured to allow a fixed amount of vCPU overcommitment by using the cpu_allocation_ratio Configuration option in nova.conf. The default setting is:

cpu_allocation_ratio=16.0

With this setting, if there are 8 vCPUs on a node, the scheduler will allow instances up to 128 vCPU to be run on that node.

To disallow vCPU overcommitment set:

cpu_allocation_ratio=1.0

Schedule 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 nova command-line tool, use the --hint flag. For example:

$ nova boot --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:

{
   "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"
      ]
   }
}

Only schedule instances on hosts if there are sufficient Disk available for ephemeral storage.

This filter can be configured to allow a fixed amount of disk overcommitment by using the disk_allocation_ratio Configuration option in nova.conf. The default setting is:

disk_allocation_ratio=1.0

Adjusting this value to be greater than 1.0 will allow scheduling instances while over committing disk resources on the node. This may be desirable if you use an image format that is sparse or copy on write such that each virtual instance does not require a 1:1 allocation of virtual disk to physical storage.

The GroupAntiAffinityFilter ensures that each instance in a group is on a different host. To take advantage of this filter, the requester must pass a scheduler hint, using group as the key and a list of instance uuids as the value. Using the nova command-line tool, use the --hint flag. For example:

$ nova boot --image cedef40a-ed67-4d10-800e-17455edce175 --flavor 1 --hint group=a0cf03a5-d921-4877-bb5c-86d26cf818e1 --hint group=8c19174f-4220-44f0-824a-cd1eeef10287 server-1

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, and virtual machine mode. E.g., an instance might require a host that runs an ARM-based processor and QEMU as the hypervisor. An image can be decorated with these properties:

$ glance image-update img-uuid --property architecture=arm --property hypervisor_type=qemu

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 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:

isolated_hosts=server1,server2
isolated_images=342b492c-128f-4a42-8d3a-c5088cf27d13,ebd267a6-ca86-4d6c-9a0e-bd132d6b7d09

The JsonFilter allows a user to construct a custom filter by passing a scheduler hint in JSON format. The following operators are supported:

The filter supports the following variables:

Using the nova command-line tool, use the --hint flag:

$ nova boot --image 827d564a-e636-4fc4-a376-d36f7ebe1747 --flavor
1 --hint query='[">=","$free_ram_mb",1024]' server1

With the API, use the os:scheduler_hints key:

{
   "server":{
      "name":"server-1",
      "imageRef":"cedef40a-ed67-4d10-800e-17455edce175",
      "flavorRef":"1"
   },
   "os:scheduler_hints":{
      "query":"[>=,$free_ram_mb,1024]"
   }
}

Only schedule instances on hosts if there is sufficient RAM available. If this filter is not set, the scheduler may over provision a host based on RAM (i.e., the RAM allocated by virtual machine instances may exceed the physical RAM).

This filter can be configured to allow a fixed amount of RAM overcommitment by using the ram_allocation_ratio configuration option in nova.conf. The default setting is:

ram_allocation_ratio=1.5

With this setting, if there is 1GB of free RAM, the scheduler will allow instances up to size 1.5GB to be run on that instance.

Filter 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 will prevent 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.

Schedule 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 nova command-line tool, use the --hint flag:

$ nova boot --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:

{
   "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"
      ]
   }
}

Schedule 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:

Using the nova command-line tool, use the --hint flag. For example, to specify the IP subnet 192.168.1.1/24

$ nova boot --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:

{
   "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"
   }
}