How to add a new DB connection

Copy    <global>
        <resources>
            <tpa_setup>
                <setup>
                    <module>Vendor_Tpa</module>
                </setup>
            </tpa_setup>
            <bot_db>
                <connection>
                    <host><![CDATA[subdomain.rds.aws.com]]></host>
                    <username><![CDATA[some_name]]></username>
                    <password><![CDATA[some_pw]]></password>
                    <dbname><![CDATA[some_db_name]]></dbname>
                    <model>mysql4</model>
                    <type>pdo_mysql</type>
                    <active>1</active>
                </connection>
            </bot_db>
        </resources>
        <!-- ... -->
     </global>

Copy        /** @var Varien_Db_Adapter_Pdo_Mysql $connection */
        $connection = Mage::getSingleton('core/resource')->getConnection('bot_db');
        $select = $connection->select()
            ->from(
                'table_name',
                [
                    'code' => 'drug_id',
                    'name' => 'description',
                    'unit_price' => 'unit_price',
                    'max_qty' => 'max_quantity',
                    'updated_at' => 'updated_at'
                ]
            )
            ->where('drug_id IN (?)', array_column($items, 'code'));
        $rows = $connection->fetchAssoc($select);