How to use boto3 ssm client to create port-forwarding session?

Question

I used the python code below to create a port-forwarding session.

But it seems like the session is getting terminated in a few minutes? Can anyone tell me if I am missing something here.

My target is to bind a remote port (80) to a local port (8888).

self._session_parameters = {
            "Target": self._instance_id,
            "DocumentName": "AWS-StartPortForwardingSession",
            "Parameters": {"portNumber"[str(self._remote_port)],
                     "localPortNumber":[str(self._remote_port)]}

 self._response = self._ssm.start_session(
            Target=self._session_parameters["Target"],
          DocumentName=self._session_parameters["DocumentName"],
            Parameters=self._session_parameters["Parameters"])
 logger.info("Received response: %s", self._response["SessionId"])

 self._session_id, self._token_value = (
            self._response["SessionId"],
            self._response["TokenValue"])