def add_dns_server(self, service_name, deployment_name, dns_server_name, address):
        '''
        Adds a DNS server definition to an existing deployment.

        service_name:
            The name of the service.
        deployment_name:
            The name of the deployment.
        dns_server_name:
            Specifies the name of the DNS server.
        address:
            Specifies the IP address of the DNS server.
        '''
        _validate_not_none('service_name', service_name)
        _validate_not_none('deployment_name', deployment_name)
        _validate_not_none('dns_server_name', dns_server_name)
        _validate_not_none('address', address)
        return self._perform_post(
            self._get_dns_server_path(service_name, deployment_name),
            _XmlSerializer.dns_server_to_xml(dns_server_name, address),
            as_async=True)
Adds a DNS server definition to an existing deployment.

        service_name:
            The name of the service.
        deployment_name:
            The name of the deployment.
        dns_server_name:
            Specifies the name of the DNS server.
        address:
            Specifies the IP address of the DNS server.