def get_conn(self):
        """
        Establish a connection to druid broker.
        """
        conn = self.get_connection(self.druid_broker_conn_id)
        druid_broker_conn = connect(
            host=conn.host,
            port=conn.port,
            path=conn.extra_dejson.get('endpoint', '/druid/v2/sql'),
            scheme=conn.extra_dejson.get('schema', 'http')
        )
        self.log.info('Get the connection to druid broker on %s', conn.host)
        return druid_broker_conn
Establish a connection to druid broker.