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Multi-Architecture Deployments¶
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 x86_64
deployment¶
Install the operating system onto all the new compute nodes.
Add the new compute nodes to
openstack_user_config.yml
.Ensure a host of each compute architecture is present in
repo-infra_hosts
inopenstack_user_config.yml
.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
(see: https://docs.openstack.org/os-traits/latest/reference/traits.html)
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>
Note
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
The
image_metadata_prefilter
setting forces the Nova scheduler to match thehw_architecture
property 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.The
image_properties_default_architecture
setting would apply in an existingx86_64
architecture cloud where previouslyhw_architecture
was 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.Warning
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.
The
image_metadata_prefilter
only looks at the HW_ARCH_XXX traits on compute hosts and finds hardware that matches the required architecture. This only happens when thehw_architecture
property is present on an image, and only if the required traits are manually added to compute hosts.The
image_properties_default_architecture
is 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 thehw_architecture
property could be scheduled to a non native architecture host and emulated.Disable QEMU Emulation
Note
This step applies particularly to existing
x86_64
environments when newaarch64
compute nodes are added and it cannot be assumed that thehw_architecure
property 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
Ideally the
hw_architecture
property is set for all uploaded images. It is mandatory to set this property for all architectures that do not matchimage_properties_default_architecture
It is recommended to set the property
hw_firmware_type='uefi'
for any images which require UEFI boot, even when this implicit with theaarch64
architecture. 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.