Drop CPU type option from libvirt compute resource provisioning

ekohl · December 19, 2023, 11:57am

This came up while reviewing recent changes in fog-libvirt. The background is that now fog-libvirt changed the default CPU type from some virtual definition to host passthrough:

Foreman exposes the CPU_TYPES options:

github.com

theforeman/foreman/blob/70b2144263dc6c3a1efdd5f26d16952b2e4266c3/app/models/compute_resources/foreman/model/libvirt.rb#L8


      
          module Foreman::Model
            class Libvirt < ComputeResource
              include ComputeResourceConsoleCommon
          
              ALLOWED_DISPLAY_TYPES = %w(vnc spice)
          
              # 'custom' is not implemented. This needs extra UI.
              CPU_MODES = %w(default host-model host-passthrough)
          
              validates :url, :format => { :with => URI::DEFAULT_PARSER.make_regexp }, :presence => true
              validates :display_type, :inclusion => { :in => ALLOWED_DISPLAY_TYPES }
          
              def self.available?
                Fog::Compute.providers.include?(:libvirt)
              end
          
              # Some getters/setters for the attrs Hash
              def display_type

Now default is host-passthrough, which makes the UI confusing. It raises the question whether CPU types are needed at all. Do we need to introduce some compatibility type, or drop it altogether?

The compatibility option is there for live migration between hosts where you can at least guarantee a common baseline CPU, but we don’t support live migrations on libvirt anyway. My suggestion would be to drop it entirely. This simplifies the UI a bit and you don’t lose anything noticeable. But perhaps I’m missing something.

Marek_Hulan · December 19, 2023, 12:37pm

I only ever had to use it when the default was not working, +1 for dropping from my perspective

ekohl · December 19, 2023, 5:27pm

I’ve opened a PR for this:

github.com/theforeman/foreman

Fixes #36999 - Drop libvirt CPU model option for VM creation

theforeman:develop ← ekohl:36999-drop-libvirt-cpu-model

opened 05:26PM - 19 Dec 23 UTC

ekohl

+1 -13

Since fog-libvirt 0.12.0 the default CPU model was some abstract type with a low… compatibility level. Since 0.12.0 it defaults to CPU passthrough, as recommended by qemu if live migration is not required (https://www.qemu.org/docs/master/system/qemu-cpu-models.html). That's not something we support today, so it should be safe to drop the CPU model selection. RFC open for this: https://community.theforeman.org/t/drop-cpu-type-option-from-libvirt-compute-resource-provisioning/36267

Looking at the patch I wonder if this is even exposed in the API.

ekohl · January 22, 2024, 3:57pm

I haven’t seen any objections, so Id like to move forward with this.