Virtual hardware¶
Fine-tuning different aspects of the hardware which are not device related (BIOS, mainboard, etc.) is sometimes necessary to allow guest operating systems to properly boot and reboot.
Machine Type¶
QEMU is able to work with two different classes of chipsets for x86_64,
so called machine types. The x86_64 chipsets are i440fx (also called
pc) and q35. They are versioned based on qemu-system-${ARCH},
following the format pc-${machine_type}-${qemu_version},
e.g.pc-i440fx-2.10 and pc-q35-2.10.
KubeVirt defaults to QEMU's newest q35 machine type. If a custom machine type is desired, it is configurable through the following structure:
metadata:
name: myvmi
spec:
domain:
machine:
# This value indicates QEMU machine type.
type: pc-q35-2.10
resources:
requests:
memory: 512M
devices:
disks:
- name: myimage
disk: {}
volumes:
- name: myimage
persistentVolumeClaim:
claimName: myclaim
BIOS/UEFI¶
All virtual machines use BIOS by default for booting.
It is possible to utilize UEFI/OVMF by setting a value via
spec.firmware.bootloader:
apiVersion: kubevirt.io/v1
kind: VirtualMachineInstance
metadata:
labels:
special: vmi-alpine-efi
name: vmi-alpine-efi
spec:
domain:
devices:
disks:
- disk:
bus: virtio
name: containerdisk
features:
smm:
enabled: true
firmware:
# this sets the bootloader type
bootloader:
efi: {}
Enabling EFI automatically enables Secure Boot,
unless the secureBoot field under efi is set to false.
Secure Boot itself requires the SMM
CPU feature to be enabled as above, which does not happen automatically,
for security reasons.
SMBIOS Firmware¶
In order to provide a consistent view on the virtualized hardware for
the guest OS, the SMBIOS UUID can be set to a constant value via
spec.firmware.uuid:
metadata:
name: myvmi
spec:
domain:
firmware:
# this sets the UUID
uuid: 5d307ca9-b3ef-428c-8861-06e72d69f223
serial: e4686d2c-6e8d-4335-b8fd-81bee22f4815
resources:
requests:
memory: 512M
devices:
disks:
- name: myimage
disk: {}
volumes:
- name: myimage
persistentVolumeClaim:
claimName: myclaim
In addition, the SMBIOS serial number can be set to a constant value via
spec.firmware.serial, as demonstrated above.
CPU¶
Note: This is not related to scheduling decisions or resource assignment.
Topology¶
Setting the number of CPU cores is possible via spec.domain.cpu.cores.
The following VM will have a CPU with 3 cores:
metadata:
name: myvmi
spec:
domain:
cpu:
# this sets the cores
cores: 3
resources:
requests:
memory: 512M
devices:
disks:
- name: myimage
disk: {}
volumes:
- name: myimage
persistentVolumeClaim:
claimName: myclaim
Labeling nodes with cpu models and cpu features¶
KubeVirt can create node selectors based on VM cpu models and features. With these node selectors, VMs will be scheduled on the nodes that support the matching VM cpu model and features.
To properly label the node, user can use Kubevirt Node-labeller, which creates all necessary labels or create node labels by himself.
Kubevirt node-labeller creates 3 types of labels: cpu models, cpu features and kvm info. It uses libvirt to get all supported cpu models and cpu features on host and then Node-labeller creates labels from cpu models.
Node-labeller supports obsolete list of cpu models and minimal baseline cpu model for features. Both features can be set via KubeVirt CR:
apiVersion: kubevirt.io/v1
kind: Kubevirt
metadata:
name: kubevirt
namespace: kubevirt
spec:
...
configuration:
obsoleteCPUModels:
486: true
pentium: true
...
Obsolete cpus will not be inserted in labels. If KubeVirt CR doesn't
contain obsoleteCPUModels variable, Labeller sets default values
("pentium, pentium2, pentium3, pentiumpro, coreduo, n270,
core2duo, Conroe, athlon, phenom, kvm32, kvm64, qemu32 and qemu64").
User can change obsoleteCPUModels by adding / removing cpu model in config map. Kubevirt then update nodes with new labels.
For homogenous cluster / clusters without live migration enabled it's possible to disable the node labeler and avoid adding labels to the nodes by adding the following annotation to the nodes:
node-labeller.kubevirt.io/skip-node.
Model¶
Note: If CPU model wasn't defined, the VM will have CPU model closest to one that used on the node where the VM is running.
Note: CPU model is case sensitive.
Setting the CPU model is possible via spec.domain.cpu.model. The
following VM will have a CPU with the Conroe model:
apiVersion: kubevirt.io/v1
kind: VirtualMachineInstance
metadata:
name: myvmi
spec:
domain:
cpu:
# this sets the CPU model
model: Conroe
...
You can check list of available models here.
When CPUNodeDiscovery feature-gate is enabled and VM has cpu model,
Kubevirt creates node selector with format:
cpu-model.node.kubevirt.io/<cpuModel>, e.g.
cpu-model.node.kubevirt.io/Conroe. When VM doesn’t have cpu
model, then no node selector is created.
Enabling default cluster cpu model¶
To enable the default cpu model, user may add the cpuModel
field in the KubeVirt CR.
apiVersion: kubevirt.io/v1
kind: KubeVirt
metadata:
name: kubevirt
namespace: kubevirt
spec:
...
configuration:
cpuModel: "EPYC"
...
Default CPU model is set when vmi doesn't have any cpu model. When vmi
has cpu model set, then vmi's cpu model is preferred. When default cpu
model is not set and vmi's cpu model is not set too, host-model will
be set. Default cpu model can be changed when kubevirt is running. When
CPUNodeDiscovery feature gate is enabled Kubevirt creates node selector
with default cpu model.
CPU model special cases¶
As special cases you can set spec.domain.cpu.model equals to: -
host-passthrough to passthrough CPU from the node to the VM
metadata:
name: myvmi
spec:
domain:
cpu:
# this passthrough the node CPU to the VM
model: host-passthrough
...
host-modelto get CPU on the VM close to the node one
metadata:
name: myvmi
spec:
domain:
cpu:
# this set the VM CPU close to the node one
model: host-model
...
See the CPU API reference for more details.
Features¶
Setting CPU features is possible via spec.domain.cpu.features and can
contain zero or more CPU features :
metadata:
name: myvmi
spec:
domain:
cpu:
# this sets the CPU features
features:
# this is the feature's name
- name: "apic"
# this is the feature's policy
policy: "require"
...
Note: Policy attribute can either be omitted or contain one of the following policies: force, require, optional, disable, forbid.
Note: In case a policy is omitted for a feature, it will default to require.
Behaviour according to Policies:
- All policies will be passed to libvirt during virtual machine creation.
- In case the feature gate "CPUNodeDiscovery" is enabled and the policy is omitted or has "require" value, then the virtual machine could be scheduled only on nodes that support this feature.
- In case the feature gate "CPUNodeDiscovery" is enabled and the policy has "forbid" value, then the virtual machine would not be scheduled on nodes that support this feature.
Full description about features and policies can be found here.
When CPUNodeDiscovery feature-gate is enabled Kubevirt creates node
selector from cpu features with format:
cpu-feature.node.kubevirt.io/<cpuFeature>, e.g.
cpu-feature.node.kubevirt.io/apic. When VM doesn’t have cpu
feature, then no node selector is created.
Clock¶
Guest time¶
Sets the virtualized hardware clock inside the VM to a specific time. Available options are
-
utc
-
timezone
See the Clock API Reference for all possible configuration options.
utc¶
If utc is specified, the VM's clock will be set to UTC.
metadata:
name: myvmi
spec:
domain:
clock:
utc: {}
resources:
requests:
memory: 512M
devices:
disks:
- name: myimage
disk: {}
volumes:
- name: myimage
persistentVolumeClaim:
claimName: myclaim
timezone¶
If timezone is specified, the VM's clock will be set to the specified
local time.
metadata:
name: myvmi
spec:
domain:
clock:
timezone: "America/New York"
resources:
requests:
memory: 512M
devices:
disks:
- name: myimage
disk: {}
volumes:
- name: myimage
persistentVolumeClaim:
claimName: myclaim
Timers¶
-
pit
-
rtc
-
kvm
-
hyperv
A pretty common timer configuration for VMs looks like this:
metadata:
name: myvmi
spec:
domain:
clock:
utc: {}
# here are the timer
timer:
hpet:
present: false
pit:
tickPolicy: delay
rtc:
tickPolicy: catchup
hyperv: {}
resources:
requests:
memory: 512M
devices:
disks:
- name: myimage
disk: {}
volumes:
- name: myimage
persistentVolumeClaim:
claimName: myclaim
hpet is disabled,pit and rtc are configured to use a specific
tickPolicy. Finally, hyperv is made available too.
See the Timer API Reference for all possible configuration options.
Note: Timer can be part of a machine type. Thus it may be necessary to explicitly disable them. We may in the future decide to add them via cluster-level defaulting, if they are part of a QEMU machine definition.
Random number generator (RNG)¶
You may want to use entropy collected by your cluster nodes inside your
guest. KubeVirt allows to add a virtio RNG device to a virtual machine
as follows.
metadata:
name: vmi-with-rng
spec:
domain:
devices:
rng: {}
For Linux guests, the virtio-rng kernel module should be loaded early
in the boot process to acquire access to the entropy source. Other
systems may require similar adjustments to work with the virtio RNG
device.
Note: Some guest operating systems or user payloads may require the
RNG device with enough entropy and may fail to boot without it. For
example, fresh Fedora images with newer kernels (4.16.4+) may require
the virtio RNG device to be present to boot to login.
Video and Graphics Device¶
By default a minimal Video and Graphics device configuration will be
applied to the VirtualMachineInstance. The video device is vga
compatible and comes with a memory size of 16 MB. This device allows
connecting to the OS via vnc.
It is possible not attach it by setting
spec.domain.devices.autoattachGraphicsDevice to false:
metadata:
name: myvmi
spec:
domain:
devices:
autoattachGraphicsDevice: false
disks:
- name: myimage
disk: {}
volumes:
- name: myimage
persistentVolumeClaim:
claimName: myclaim
VMIs without graphics and video devices are very often referenced as
headless VMIs.
If using a huge amount of small VMs this can be helpful to increase the VMI density per node, since no memory needs to be reserved for video.
Features¶
KubeVirt supports a range of virtualization features which may be tweaked in order to allow non-Linux based operating systems to properly boot. Most noteworthy are
-
acpi
-
apic
-
hyperv
A common feature configuration is shown by the following example:
apiVersion: kubevirt.io/v1
kind: VirtualMachineInstance
metadata:
name: myvmi
spec:
domain:
# typical features
features:
acpi: {}
apic: {}
hyperv:
relaxed: {}
vapic: {}
spinlocks:
spinlocks: 8191
resources:
requests:
memory: 512M
devices:
disks:
- name: myimage
disk: {}
volumes:
- name: myimage
persistentVolumeClaim:
claimname: myclaim
See the Features API Reference for all available features and configuration options.
Resources Requests and Limits¶
An optional resource request can be specified by the users to allow the scheduler to make a better decision in finding the most suitable Node to place the VM.
apiVersion: kubevirt.io/v1
kind: VirtualMachineInstance
metadata:
name: myvmi
spec:
domain:
resources:
requests:
memory: "1Gi"
cpu: "1"
limits:
memory: "2Gi"
cpu: "2"
disks:
- name: myimage
disk: {}
volumes:
- name: myimage
persistentVolumeClaim:
claimname: myclaim
CPU¶
Specifying CPU limits will determine the amount of cpu shares set on the control group the VM is running in, in other words, the amount of time the VM's CPUs can execute on the assigned resources when there is a competition for CPU resources.
For more information please refer to how Pods with resource limits are run.
Memory Overhead¶
Various VM resources, such as a video adapter, IOThreads, and supplementary system software, consume additional memory from the Node, beyond the requested memory intended for the guest OS consumption. In order to provide a better estimate for the scheduler, this memory overhead will be calculated and added to the requested memory.
Please see how Pods with resource requests are scheduled for additional information on resource requests and limits.
Hugepages¶
KubeVirt give you possibility to use hugepages as backing memory for
your VM. You will need to provide desired amount of memory
resources.requests.memory and size of hugepages to use
memory.hugepages.pageSize, for example for x86_64 architecture it can
be 2Mi.
apiVersion: kubevirt.io/v1alpha1
kind: VirtualMachine
metadata:
name: myvm
spec:
domain:
resources:
requests:
memory: "64Mi"
memory:
hugepages:
pageSize: "2Mi"
disks:
- name: myimage
disk: {}
volumes:
- name: myimage
persistentVolumeClaim:
claimname: myclaim
In the above example the VM will have 64Mi of memory, but instead of
regular memory it will use node hugepages of the size of 2Mi.
Limitations¶
-
a node must have pre-allocated hugepages
-
hugepages size cannot be bigger than requested memory
-
requested memory must be divisible by hugepages size
-
hugepages uses by default memfd. Memfd is supported from kernel >= 4.14. If you run on an older host (e.g centos 7.9), it is required to disable memfd with the annotation
kubevirt.io/memfd: "false"in the VMI metadata annotation.
Input Devices¶
Tablet¶
Kubevirt supports input devices. The only type which is supported is
tablet. Tablet input device supports only virtio and usb bus. Bus
can be empty. In that case, usb will be selected.