def __virtual__():
    try:
        if salt.utils.is_proxy() and __opts__['proxy']['proxytype'] == 'rest_sample':
            return __virtualname__
    except KeyError:
        return (False, 'The rest_package execution module failed to load.  Check the proxy key in pillar.')

    return (False, 'The rest_package execution module failed to load: only works on a rest_sample proxy minion.')
Only work on systems that are a proxy minion
dataset/ETHPy150Open saltstack/salt/salt/modules/rest_package.py/__virtual__