def create_instance(self, name, template, args=None, labels=None):
        """
        Create a new instance based on an existing template. This method blocks
        until the instance is fully started.

        :param str instance: A Yamcs instance name.
        :param str template: The name of an existing template.
        """
        req = rest_pb2.CreateInstanceRequest()
        req.name = name
        req.template = template
        if args:
            for k in args:
                req.templateArgs[k] = args[k]
        if labels:
            for k in labels:
                req.labels[k] = labels[k]
        url = '/instances'
        self.post_proto(url, data=req.SerializeToString())
Create a new instance based on an existing template. This method blocks
        until the instance is fully started.

        :param str instance: A Yamcs instance name.
        :param str template: The name of an existing template.