@classmethod
def restart(cls, resources, background=False):
    """Restart a PaaS instance."""
    if not isinstance(resources, (list, tuple)):
        resources = [resources]
    opers = []
    for item in resources:
        oper = cls.call('paas.restart', cls.usable_id(item))
        if isinstance(oper, list):
            opers.extend(oper)
        else:
            opers.append(oper)
    if background:
        return opers
    cls.echo('Restarting your PaaS instance.')
    cls.display_progress(opers)
