OpenStack-Ansible supports deployments where either the control plane or compute nodes may comprise of several different CPU architectures
Mixed CPU architectures for compute nodes¶
OpenStack-Ansible supports having compute nodes of multiple architectures deployed in the same environment.
Deployments consisting entirely of x86_64 or aarch64 nodes do not need any special consideration and will work according to the normal OpenStack-Ansible documentation.
A deployment with a mixture of architectures, or adding a new architecture to an existing single architecure deployment requires some additional steps to be taken by both the deployer and end users to ensure that the behaviour is as desired.
Example - adding
aarch64 nodes to an
Install the operating system onto all the new compute nodes.
Add the new compute nodes to
Ensure a host of each compute architecture is present in
This host will build python wheels for it's own architecture which will speed up the deployment of many hosts. If you do not make a repository server for each architecture, ensure that measures are taken not to overload the opendev.org git servers, such as using local mirrors of all OpenStack service repos.
Run the OpenStack-Ansible playbooks to deploy the required services.
Add HW_ARCH_XXXX Trait to Every Compute Host in Openstack
Although most CPU hardware traits such as instruction set extensions are detected and handled automatically in OpenStack, CPU architecture is not. It is necessary to manually add an architecture trait to the resource provider corresponding to every compute host. The required traits are:
HW_ARCH_X86_64 for x86_64 Intel and AMD CPUs HW_ARCH_AARCH64 for aarch64 architecure CPUs
openstack resource provider list openstack resource provider trait list <uuid-of-compute-host> openstack resource provider trait set --trait <existing-trait-1> --trait <existing-trait-2> ... --trait HW_ARCH_xxxxx <uuid-of-compute-host>
The trait set command replaces all existing traits with the set provided, so you must specify all existing traits as well as the new trait.
Configure Nova Scheduler to Check Architecture
Two additional settings in /etc/nova/nova.conf in all Nova API instances:
[scheduler] image_metadata_prefilter = True [filter_scheduler] image_properties_default_architecture = x86_64
image_metadata_prefiltersetting forces the Nova scheduler to match the
hw_architectureproperty on Glance images with the corresponding HW_ARCH_XXX trait on compute host resource providers. This ensures that images explicitly tagged with a target architecture get scheduled hosts with a matching architecture.
image_properties_default_architecturesetting would apply in an existing
x86_64architecture cloud where previously
hw_architecturewas not set on all Glance images. This avoids the need to retrospectively apply the property for all existing images which may be difficult as users may have their own tooling to create and upload images without applying the required property.
Undocumented Behaviour Alert!
Note that the image metadata prefilter and ImagePropertiesFilter are different and unrelated steps in the process Nova scheduler uses to determine candidate compute hosts. This section explains how to use them together.
image_metadata_prefilteronly looks at the HW_ARCH_XXX traits on compute hosts and finds hardware that matches the required architecture. This only happens when the
hw_architectureproperty is present on an image, and only if the required traits are manually added to compute hosts.
image_properties_default_architectureis used by the ImagePropertiesFilter which examines all the architectures supported by QEMU on each compute host; this includes software emulations of non-native architectures.
If the full QEMU suite is installed on a compute host, that host will offer to run all architectures supported by the available
qemu-system-*binaries. In this situation images without the
hw_architectureproperty could be scheduled to a non native architecture host and emulated.
Disable QEMU Emulation
This step applies particularly to existing
x86_64environments when new
aarch64compute nodes are added and it cannot be assumed that the
hw_architecureproperty is applied to all Glance images as the operator may not be in control of all image uploads.
To avoid unwanted QEMU emulation of non native architectures it is necessary to ensure that only the native
qemu-system-*binary is present on all compute nodes. The simplest way to do this for existing deployments is to use the system package manager to ensure that the unwanted binaries are removed.
OpenStack-Ansible releases including 2023.1 and later will only install the native architecture qemu-system-*` binary so this step should not be required on newer releases.
Upload images to Glance
hw_architectureproperty is set for all uploaded images. It is mandatory to set this property for all architectures that do not match
It is recommended to set the property
hw_firmware_type='uefi'for any images which require UEFI boot, even when this implicit with the
aarch64architecture. This is to avoid issues with NVRAM files in libvirt when deleting an instance.
Architecture emulation by Nova¶
Nova has the capability to allow emulation of one CPU architecture on a host with a different native CPU architecure, see https://docs.openstack.org/nova/latest/admin/hw-emulation-architecture.html for more details.
This OpenStack-Ansible documentation currently assumes that a deployer wishes to run images on a compute host with a native CPU architecure, and does not give an example configuration involving emulation.