def get_limits(self):
        """
        Return all known limits for this service, as a dict of their names
        to :py:class:`~.AwsLimit` objects.

        :returns: dict of limit names to :py:class:`~.AwsLimit` objects
        :rtype: dict
        """
        if self.limits != {}:
            return self.limits
        limits = {}
        limits['DB instances'] = AwsLimit(
            'DB instances',
            self,
            40,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBInstance'
        )
        limits['Reserved Instances'] = AwsLimit(
            'Reserved Instances',
            self,
            40,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBInstance',
        )
        limits['Storage quota (GB)'] = AwsLimit(
            'Storage quota (GB)',
            self,
            100000,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBInstance',
        )
        limits['DB snapshots per user'] = AwsLimit(
            'DB snapshots per user',
            self,
            100,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBSnapshot',
        )
        limits['DB parameter groups'] = AwsLimit(
            'DB parameter groups',
            self,
            50,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBParameterGroup',
        )
        limits['DB security groups'] = AwsLimit(
            'DB security groups',
            self,
            25,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBSecurityGroup',
        )
        limits['VPC Security Groups'] = AwsLimit(
            'VPC Security Groups',
            self,
            5,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBSecurityGroup',
        )
        limits['Subnet Groups'] = AwsLimit(
            'Subnet Groups',
            self,
            50,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBSubnetGroup',
            ta_limit_name='Subnet groups'
        )
        limits['Subnets per Subnet Group'] = AwsLimit(
            'Subnets per Subnet Group',
            self,
            20,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBSubnetGroup',
            ta_limit_name='Subnets per subnet group'
        )
        limits['Option Groups'] = AwsLimit(
            'Option Groups',
            self,
            20,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBOptionGroup',
        )
        limits['Event Subscriptions'] = AwsLimit(
            'Event Subscriptions',
            self,
            20,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBEventSubscription',
            ta_limit_name='Event subscriptions'
        )
        limits['Read replicas per master'] = AwsLimit(
            'Read replicas per master',
            self,
            5,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBInstance',
        )
        # this is the number of rules per security group
        limits['Max auths per security group'] = AwsLimit(
            'Max auths per security group',
            self,
            20,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBSecurityGroup',
            limit_subtype='AWS::RDS::DBSecurityGroupIngress',
        )
        limits['DB Clusters'] = AwsLimit(
            'DB Clusters',
            self,
            40,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBCluster',
            ta_limit_name='Clusters'
        )
        limits['DB Cluster Parameter Groups'] = AwsLimit(
            'DB Cluster Parameter Groups',
            self,
            50,
            self.warning_threshold,
            self.critical_threshold,
            limit_type='AWS::RDS::DBClusterParameterGroup',
            ta_limit_name='Cluster parameter groups'
        )
        self.limits = limits
        return limits