openstack-manuals/doc/admin-guide-cloud/source/compute-flavors.rst

Flavors

Admin users can use the nova flavor- commands to customize and manage flavors. To see the available flavor-related commands, run:

$ nova help | grep flavor-
  flavor-access-add     Add flavor access for the given tenant.
  flavor-access-list    Print access information about the given flavor.
  flavor-access-remove  Remove flavor access for the given tenant.
  flavor-create         Create a new flavor
  flavor-delete         Delete a specific flavor
  flavor-key            Set or unset extra_spec for a flavor.
  flavor-list           Print a list of available 'flavors' (sizes of
  flavor-show           Show details about the given flavor.

Note

• Configuration rights can be delegated to additional users by redefining the access controls for compute_extension:flavormanage in /etc/nova/policy.json on the nova-api server.
• To modify an existing flavor in the dashboard, you must delete the flavor and create a modified one with the same name.

Flavors define these elements:

Element	Description
Name	A descriptive name. XX.SIZE_NAME is typically not required, though some third party tools may rely on it.
Memory_MB	Virtual machine memory in megabytes.
Disk	Virtual root disk size in gigabytes. This is an ephemeral disk that the base image is copied into. When booting from a persistent volume it is not used. The "0" size is a special case which uses the native base image size as the size of the ephemeral root volume.
Ephemeral	Specifies the size of a secondary ephemeral data disk. This is an empty, unformatted disk and exists only for the life of the instance.
Swap	Optional swap space allocation for the instance.
VCPUs	Number of virtual CPUs presented to the instance.
RXTX_Factor	Optional property allows created servers to have a different bandwidth cap than that defined in the network they are attached to. This factor is multiplied by the rxtx_base property of the network. Default value is 1.0. That is, the same as attached network. This parameter is only available for Xen or NSX based systems.
Is_Public	Boolean value, whether flavor is available to all users or private to the tenant it was created in. Defaults to True.
extra_specs	Key and value pairs that define on which compute nodes a flavor can run. These pairs must match corresponding pairs on the compute nodes. Use to implement special resources, such as flavors that run on only compute nodes with GPU hardware.

Flavor customization can be limited by the hypervisor in use. For example the libvirt driver enables quotas on CPUs available to a VM, disk tuning, bandwidth I/O, watchdog behavior, random number generator device control, and instance VIF traffic control.

CPU limits

You can configure the CPU limits with control parameters with the nova client. For example, to configure the I/O limit, use:

$ nova flavor-key m1.small set quota:read_bytes_sec=10240000
$ nova flavor-key m1.small set quota:write_bytes_sec=10240000

Use these optional parameters to control weight shares, enforcement intervals for runtime quotas, and a quota for maximum allowed bandwidth:

• cpu_shares. Specifies the proportional weighted share for the domain. If this element is omitted, the service defaults to the OS provided defaults. There is no unit for the value; it is a relative measure based on the setting of other VMs. For example, a VM configured with value 2048 gets twice as much CPU time as a VM configured with value 1024.

• cpu_shares_level. On VMWare, specifies the allocation level. Can be custom, high, normal, or low. If you choose custom, set the number of shares using cpu_shares_share.

• cpu_period. Specifies the enforcement interval (unit: microseconds) for QEMU and LXC hypervisors. Within a period, each VCPU of the domain is not allowed to consume more than the quota worth of runtime. The value should be in range [1000, 1000000]. A period with value 0 means no value.

• cpu_limit. Specifies the upper limit for VMware machine CPU allocation in MHz. This parameter ensures that a machine never uses more than the defined amount of CPU time. It can be used to enforce a limit on the machine's CPU performance.

• cpu_reservation. Specifies the guaranteed minimum CPU reservation in MHz for VMware. This means that if needed, the machine will definitely get allocated the reserved amount of CPU cycles.

• cpu_quota. Specifies the maximum allowed bandwidth (unit: microseconds). A domain with a negative-value quota indicates that the domain has infinite bandwidth, which means that it is not bandwidth controlled. The value should be in range [1000, 18446744073709551] or less than 0. A quota with value 0 means no value. You can use this feature to ensure that all vCPUs run at the same speed. For example:

  $ nova flavor-key m1.low_cpu set quota:cpu_quota=10000
  $ nova flavor-key m1.low_cpu set quota:cpu_period=20000

  In this example, the instance of m1.low_cpu can only consume a maximum of 50% CPU of a physical CPU computing capability.

Disk tuning

Using disk I/O quotas, you can set maximum disk write to 10 MB per second for a VM user. For example:

$ nova flavor-key m1.medium set quota:disk_write_bytes_sec=10485760

The disk I/O options are:

• disk_read_bytes_sec
• disk_read_iops_sec
• disk_write_bytes_sec
• disk_write_iops_sec
• disk_total_bytes_sec
• disk_total_iops_sec

Bandwidth I/O

The vif I/O options are:

• vif_inbound_ average
• vif_inbound_burst
• vif_inbound_peak
• vif_outbound_ average
• vif_outbound_burst
• vif_outbound_peak

Incoming and outgoing traffic can be shaped independently. The bandwidth element can have at most, one inbound and at most, one outbound child element. If you leave any of these child elements out, no quality of service (QoS) is applied on that traffic direction. So, if you want to shape only the network's incoming traffic, use inbound only (and vice versa). Each element has one mandatory attribute average, which specifies the average bit rate on the interface being shaped.

There are also two optional attributes (integer): peak, which specifies the maximum rate at which a bridge can send data (kilobytes/second), and burst, the amount of bytes that can be burst at peak speed (kilobytes). The rate is shared equally within domains connected to the network.

The example below sets network traffic bandwidth limits for existing flavor as follows:

• Outbound traffic:
  • average: 256 Mbps (32768 kilobytes/second)
  • peak: 512 Mbps (65536 kilobytes/second)
  • burst: 65536 kilobytes
• Inbound traffic:
  • average: 256 Mbps (32768 kilobytes/second)
  • peak: 512 Mbps (65536 kilobytes/second)
  • burst: 65536 kilobytes

$ nova flavor-key nlimit set quota:vif_outbound_average=32768
$ nova flavor-key nlimit set quota:vif_outbound_peak=65536
$ nova flavor-key nlimit set quota:vif_outbound_burst=65536
$ nova flavor-key nlimit set quota:vif_inbound_average=32768
$ nova flavor-key nlimit set quota:vif_inbound_peak=65536
$ nova flavor-key nlimit set quota:vif_inbound_burst=65536

Note

All the speed limit values in above example are specified in kilobytes/second. And burst values are in kilobytes.

Watchdog behavior

For the libvirt driver, you can enable and set the behavior of a virtual hardware watchdog device for each flavor. Watchdog devices keep an eye on the guest server, and carry out the configured action, if the server hangs. The watchdog uses the i6300esb device (emulating a PCI Intel 6300ESB). If hw:watchdog_action is not specified, the watchdog is disabled.

To set the behavior, use:

$ nova flavor-key FLAVOR-NAME set hw:watchdog_action=ACTION

Valid ACTION values are:

• disabled—(default) The device is not attached.
• reset—Forcefully reset the guest.
• poweroff—Forcefully power off the guest.
• pause—Pause the guest.
• none—Only enable the watchdog; do nothing if the server hangs.

Note

Watchdog behavior set using a specific image's properties will override behavior set using flavors.

Random-number generator

If a random-number generator device has been added to the instance through its image properties, the device can be enabled and configured using:

$ nova flavor-key FLAVOR-NAME set hw_rng:allowed=True
$ nova flavor-key FLAVOR-NAME set hw_rng:rate_bytes=RATE-BYTES
$ nova flavor-key FLAVOR-NAME set hw_rng:rate_period=RATE-PERIOD

Where:

• RATE-BYTES—(Integer) Allowed amount of bytes that the guest can read from the host's entropy per period.
• RATE-PERIOD—(Integer) Duration of the read period in seconds.

CPU toplogy

For the libvirt driver, you can define the topology of the processors in the virtual machine using properties. The properties with max limit the number that can be selected by the user with image properties.

$ nova flavor-key FLAVOR-NAME set hw:cpu_sockets=FLAVOR-SOCKETS
$ nova flavor-key FLAVOR-NAME set hw:cpu_cores=FLAVOR-CORES
$ nova flavor-key FLAVOR-NAME set hw:cpu_threads=FLAVOR-THREADS
$ nova flavor-key FLAVOR-NAME set hw:cpu_max_sockets=FLAVOR-SOCKETS
$ nova flavor-key FLAVOR-NAME set hw:cpu_max_cores=FLAVOR-CORES
$ nova flavor-key FLAVOR-NAME set hw:cpu_max_threads=FLAVOR-THREADS

Where:

• FLAVOR-SOCKETS—(Integer) The number of sockets for the guest VM. By this is set to the number of vCPUs requested.
• FLAVOR-CORES—(Integer) The number of cores per socket for the guest VM. By this is set to 1.
• FLAVOR-THREADS—(Integer) The number of threads per core for the guest VM. By this is set to 1.

Project private flavors

Flavors can also be assigned to particular projects. By default, a flavor is public and available to all projects. Private flavors are only accessible to those on the access list and are invisible to other projects. To create and assign a private flavor to a project, run these commands:

$ nova flavor-create --is-public false p1.medium auto 512 40 4
$ nova flavor-access-add 259d06a0-ba6d-4e60-b42d-ab3144411d58 86f94150ed744e08be565c2ff608eef9