To ensure that a newly created virtual machine has network access you must create and attach a vNIC.

This Ruby example creates a vNIC and attaches it to an existing virtual machine, myvm.

# Find the root of the tree of services:
system_service = connection.system_service

# Find the virtual machine:
vms_service = system_service.vms_service
vm = vms_service.list(search: 'name=myvm').first

# In order to specify the network that the new NIC will be connected to, you must
# specify the identifier of the vNIC profile. However, there may be multiple
# profiles with the same name (for different data centers, for example), so first
# you must find the networks that are available in the cluster that the
# virtual machine belongs to.
cluster = connection.follow_link(vm.cluster)
networks = connection.follow_link(cluster.networks)
network_ids = networks.map(&:id)

# Now that you know what networks are available in the cluster, you can select a
# vNIC profile that corresponds to one of those networks, and has the
# name that you want to use. The system automatically creates a vNIC
# profile for each network, with the same name as the network.
profiles_service = system_service.vnic_profiles_service
profiles = profiles_service.list
profile = profiles.detect { |p| network_ids.include?(p.network.id) && p.name == 'myprofile' }

# Locate the service that manages the network interface cards collection of the
# virtual machine:
nics_service = vms_service.vm_service(vm.id).nics_service

# Add the new network interface card:
nics_service.add(
  OvirtSDK4::Nic.new(
    name: 'mynic',
    description: 'My network interface card',
    vnic_profile: {
      id: profile.id
    }
  )
)

For more information, see http://www.rubydoc.info/gems/ovirt-engine-sdk/OvirtSDK4/VmsService:add.