Admin users can use the openstack flavor command to customize and manage flavors. To see information for this command, run:
$ openstack flavor --help Command "flavor" matches: flavor create flavor delete flavor list flavor set flavor show flavor unset
Flavors define these elements:
|Name||A descriptive name. XX.SIZE_NAME is typically not required, though some third party tools may rely on it.|
|Memory MB||Instance 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. However, in this case the filter scheduler cannot select the compute host based on the virtual image size. Therefore 0 should only be used for volume booted instances or for testing purposes.|
|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. Default value is
|Swap||Optional swap space allocation for the instance. Default
|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
|Is Public||Boolean value, whether flavor is available to all users or private to the project it was created in. Defaults to
|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.
Flavors can 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 this command:
$ openstack flavor create --private p1.medium --id auto --ram 512 --disk 40 --vcpus 4
You can configure the CPU limits with control parameters with the
nova client. For example, to configure the I/O limit, use:
$ openstack flavor set FLAVOR-NAME \ --property quota:read_bytes_sec=10240000 \ --property 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
low. If you choose
custom, set the number of shares using
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
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
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
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:
$ openstack flavor set FLAVOR-NAME \ --property quota:cpu_quota=10000 \ --property quota:cpu_period=20000
In this example, an instance of
FLAVOR-NAME can only consume
a maximum of 50% CPU of a physical CPU computing capability.
For VMware, you can configure the memory limits with control parameters.
Use these optional parameters to limit the memory allocation, guarantee minimum memory reservation, and to specify shares used in case of resource contention:
memory_limit: Specifies the upper limit for VMware machine
memory allocation in MB. The utilization of a virtual machine will
not exceed this limit, even if there are available resources. This
is typically used to ensure a consistent performance of
virtual machines independent of available resources.
memory_reservation: Specifies the guaranteed minimum memory
reservation in MB for VMware. This means the specified amount of
memory will definitely be allocated to the machine.
memory_shares_level: On VMware, specifies the allocation level.
This can be
low. If you choose
custom, set the number of shares using
memory_shares_share: Specifies the number of shares allocated
in the event that
custom is used. There is no unit for this
value. It is a relative measure based on the settings for other VMs.
$ openstack flavor set FLAVOR-NAME \ --property quota:memory_shares_level=custom \ --property quota:memory_shares_share=15
For VMware, you can configure the resource limits for disk with control parameters.
Use these optional parameters to limit the disk utilization, guarantee disk allocation, and to specify shares used in case of resource contention. This allows the VMware driver to enable disk allocations for the running instance.
disk_io_limit: Specifies the upper limit for disk
utilization in I/O per second. The utilization of a
virtual machine will not exceed this limit, even
if there are available resources. The default value
is -1 which indicates unlimited usage.
disk_io_reservation: Specifies the guaranteed minimum disk
allocation in terms of IOPS.
disk_io_shares_level: Specifies the allocation
level. This can be
If you choose custom, set the number of shares
disk_io_shares_share: Specifies the number of shares
allocated in the event that
custom is used.
When there is resource contention, this value is used
to determine the resource allocation.
The example below sets the
disk_io_reservation to 2000 IOPS.
$ openstack flavor set FLAVOR-NAME \ --property quota:disk_io_reservation=2000
Using disk I/O quotas, you can set maximum disk write to 10 MB per second for a VM user. For example:
$ openstack flavor set FLAVOR-NAME \ --property quota:disk_write_bytes_sec=10485760
The disk I/O options are:
The vif I/O options are:
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):
specifies the maximum rate at which a bridge can send data
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:
$ openstack flavor set FLAVOR-NAME \ --property quota:vif_outbound_average=32768 \ --property quota:vif_outbound_peak=65536 \ --property quota:vif_outbound_burst=65536 \ --property quota:vif_inbound_average=32768 \ --property quota:vif_inbound_peak=65536 \ --property quota:vif_inbound_burst=65536
All the speed limit values in above example are specified in kilobytes/second. And burst values are in kilobytes. Values were converted using ‘Data rate units on Wikipedia <https://en.wikipedia.org/wiki/Data_rate_units>`_.
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:
$ openstack flavor set FLAVOR-NAME --property 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.
Watchdog behavior set using a specific image’s properties will override behavior set using flavors.
If a random-number generator device has been added to the instance through its image properties, the device can be enabled and configured using:
$ openstack flavor set FLAVOR-NAME \ --property hw_rng:allowed=True \ --property hw_rng:rate_bytes=RATE-BYTES \ --property hw_rng:rate_period=RATE-PERIOD
For the libvirt driver, you can define the topology of the processors
in the virtual machine using properties. The properties with
limit the number that can be selected by the user with image properties.
$ openstack flavor set FLAVOR-NAME \ --property hw:cpu_sockets=FLAVOR-SOCKETS \ --property hw:cpu_cores=FLAVOR-CORES \ --property hw:cpu_threads=FLAVOR-THREADS \ --property hw:cpu_max_sockets=FLAVOR-SOCKETS \ --property hw:cpu_max_cores=FLAVOR-CORES \ --property hw:cpu_max_threads=FLAVOR-THREADS
For the libvirt driver, you can pin the virtual CPUs (vCPUs) of instances to the host’s physical CPU cores (pCPUs) using properties. You can further refine this by stating how hardware CPU threads in a simultaneous multithreading-based (SMT) architecture be used. These configurations will result in improved per-instance determinism and performance.
SMT-based architectures include Intel processors with Hyper-Threading technology. In these architectures, processor cores share a number of components with one or more other cores. Cores in such architectures are commonly referred to as hardware threads, while the cores that a given core share components with are known as thread siblings.
Host aggregates should be used to separate these pinned instances from unpinned instances as the latter will not respect the resourcing requirements of the former.
$ openstack flavor set FLAVOR-NAME \ --property hw:cpu_policy=CPU-POLICY \ --property hw:cpu_thread_policy=CPU-THREAD-POLICY
Valid CPU-POLICY values are:
shared: (default) The guest vCPUs will be allowed to freely float across host pCPUs, albeit potentially constrained by NUMA policy.
dedicated: The guest vCPUs will be strictly pinned to a set of host pCPUs. In the absence of an explicit vCPU topology request, the drivers typically expose all vCPUs as sockets with one core and one thread. When strict CPU pinning is in effect the guest CPU topology will be setup to match the topology of the CPUs to which it is pinned. This option implies an overcommit ratio of 1.0. For example, if a two vCPU guest is pinned to a single host core with two threads, then the guest will get a topology of one socket, one core, two threads.
Valid CPU-THREAD-POLICY values are:
prefer: (default) The host may or may not have an SMT architecture. Where an SMT architecture is present, thread siblings are preferred.
isolate: The host must not have an SMT architecture or must emulate a non-SMT architecture. If the host does not have an SMT architecture, each vCPU is placed on a different core as expected. If the host does have an SMT architecture - that is, one or more cores have thread siblings - then each vCPU is placed on a different physical core. No vCPUs from other guests are placed on the same core. All but one thread sibling on each utilized core is therefore guaranteed to be unusable.
require: The host must have an SMT architecture. Each vCPU is allocated on thread siblings. If the host does not have an SMT architecture, then it is not used. If the host has an SMT architecture, but not enough cores with free thread siblings are available, then scheduling fails.
hw:cpu_thread_policy option is only valid if
is set to
For the libvirt driver, you can define the host NUMA placement for the instance vCPU threads as well as the allocation of instance vCPUs and memory from the host NUMA nodes. For flavors whose memory and vCPU allocations are larger than the size of NUMA nodes in the compute hosts, the definition of a NUMA topology allows hosts to better utilize NUMA and improve performance of the instance OS.
$ openstack flavor set FLAVOR-NAME \ --property hw:numa_nodes=FLAVOR-NODES \ --property hw:numa_cpus.N=FLAVOR-CORES \ --property hw:numa_mem.N=FLAVOR-MEMORY
hw:numa_mem.N are only valid if
hw:numa_nodes is set. Additionally, they are only required if the
instance’s NUMA nodes have an asymmetrical allocation of CPUs and RAM
(important for some NFV workloads).
N parameter is an index of guest NUMA nodes and may not
correspond to host NUMA nodes. For example, on a platform with two
NUMA nodes, the scheduler may opt to place guest NUMA node 0, as
hw:numa_mem.0 on host NUMA node 1 and vice versa.
Similarly, the integers used for
FLAVOR-CORES are indexes of
guest vCPUs and may not correspond to host CPUs. As such, this
feature cannot be used to constrain instances to specific host CPUs or
If the combined values of
are greater than the available number of CPUs or memory respectively,
an exception is raised.
You can configure the size of large pages used to back the VMs.
$ openstack flavor set FLAVOR-NAME \ --property hw:mem_page_size=PAGE_SIZE
PAGE_SIZE values are:
small: (default) The smallest page size is used. Example: 4 KB on x86.
large: Only use larger page sizes for guest RAM. Example: either 2 MB or 1 GB on x86.
any: It is left up to the compute driver to decide. In this case, the libvirt driver might try to find large pages, but fall back to small pages. Other drivers may choose alternate policies for
Large pages can be enabled for guest RAM without any regard to whether the guest OS will use them or not. If the guest OS chooses not to use huge pages, it will merely see small pages as before. Conversely, if a guest OS does intend to use huge pages, it is very important that the guest RAM be backed by huge pages. Otherwise, the guest OS will not be getting the performance benefit it is expecting.
You can assign PCI devices to a guest by specifying them in the flavor.
$ openstack flavor set FLAVOR-NAME \ --property pci_passthrough:alias=ALIAS:COUNT
When your Compute services use the Hyper-V hypervisor, you can enable secure boot for Windows and Linux instances.
$ openstack flavor set FLAVOR-NAME \ --property os:secure_boot=SECURE_BOOT_OPTION
SECURE_BOOT_OPTION values are:
required: Enable Secure Boot for instances running with this flavor.
optional: (default) Disable Secure Boot for instances running with this flavor.