def METHOD_NAME(username, hostname):
    """
    Join a Riak cluster
    .. versionchanged:: 2015.8.0
    CLI Example:
    .. code-block:: bash
        salt '*' riak.cluster_join <user> <host>
    username - The riak username to join the cluster
    hostname - The riak hostname you are connecting to
    """
    ret = {"comment": "", "success": False}
    cmd = __execute_cmd("riak-admin", "cluster join {}@{}".format(username, hostname))
    if cmd["retcode"] != 0:
        ret["comment"] = cmd["stdout"]
    else:
        ret["comment"] = cmd["stdout"]
        ret["success"] = True
    return ret