How could we tell which interface is primary? IIRC Foreman prefers physical interfaces over virtual. If you provision host from pure Foreman, you always choose which interface is primary explicit/
ly. The same issue is there though, when host is created based on facts import... perhaps in case of discovery. I thought discovery prefered interface specified in bootif. Would custom fact be a solution?

Here is the test that is failing, put it into host_test.rb and see yourself. Will take a quick look tomorrow, but I have other priorities, so will leave it here as is:

    test "#set_interfaces sets previously detected VLAN as primary interface " do
      host = FactoryBot.create(:host, :hostgroup => FactoryBot.create(:hostgroup), :mac => '00:00:00:11:22:33')
      hash = { :eth0 => {:macaddress => '00:00:00:44:55:66', :mtu => 1500, :link => true},
               :eth0_42 => {:macaddress => '00:00:00:44:55:77', :ipaddress => '10.10.0.1', :virtual => false, :attached_to => "eth0", :tag => "42"}
      }.with_indifferent_access
      parser = stub(:interfaces => hash, :ipmi_interface => {}, :suggested_primary_interface => hash.to_a.last)
      host.set_interfaces(parser)
      assert_equal 'eth0_42', host.primary_interface.identifier
      assert_equal '00:00:00:44:55:77', host.primary_interface.mac
      assert_equal '10.10.0.1', host.primary_interface.ip
    end