Filters

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

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

Filters hosts by flavor (also known as instance type). The scheduler will check to ensure that a host has sufficient capabilities for the requested flavor. 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 overprovision 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 keyand 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-86d26cf818e1,8c19174f-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'],
    }
}

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 overprovision 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.

	Warning
	The ram_allocation_ratio option does not work properly in the Essex release, see bug #1016273 for details.

Schedule the instance on the same host as another instance in a set of 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-86d26cf818e1,8c19174f-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'],
    }
}

	Warning
	The SimpleCIDRAffinityFilter does not work properly in the Essex release. See bug 999928 for details.

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'
    }
}