SSH tunnel from Python is closing automatically

Question

I need some advice about the structure of my program. I'm connecting to an external MySQL database using sshtunnel . It's now working correctly (I can issue SQL commands and get results) but only if the commands are in the same function as the opening of the connection. If they're in a different function, the tunnel closes automatically before I can use it. (See code below - it closes between the two checkpoints.) So my questions are:

1. Should I check that the connection is open every time I want to use it? How do I do that?
2. How do I use the connection from a different function? I've seen a property called "keepalive" in sshtunnel (which will keep the connection open for a specified length of time) - is this what I need? How do I use it?
3. Can I forget about closing the tunnel manually?
4. Anything else that would help me get this working? As you can probably tell, I'm a newbie on the subject!

Thanks.

Python script:

import pymysql, shlex, shutil, subprocess
import logging
import sshtunnel
from sshtunnel import SSHTunnelForwarder
import iot_config as cfg

def OpenRemoteDB():
    global remotecur, remotedb
    sshtunnel.DEFAULT_LOGLEVEL = logging.DEBUG
    with SSHTunnelForwarder(
            (cfg.sshconn['host'], cfg.sshconn['port']),
            ssh_username = cfg.sshconn['user'],
            ssh_private_key = cfg.sshconn['private_key_loc'],
            ssh_private_key_password = cfg.sshconn['private_key_passwd'],
            remote_bind_address = ('127.0.0.1', 3306)) as server:
        remotedb = None
        remotedb = pymysql.connect(host='127.0.0.1', user=cfg.remotedbconn['user'], passwd=cfg.remotedbconn['passwd'], db=cfg.remotedbconn['db'], port=server.local_bind_port)
        remotecur = remotedb.cursor()
        print("Checkpoint 1")
        #The next three lines work fine
#        remotecur.execute("SELECT ActionID, Description FROM cmAction")
#        for r in remotecur:
#            print(r)

def SyncActions():
    print("Checkpoint 2")
    #the next three lines don't work (because the connection has closed)
    remotecur.execute("SELECT ActionID, Description FROM cmAction")
    for r in remotecur:
        print(r)

# Main program starts here
OpenRemoteDB()
SyncActions()

Output:

2016-10-06 12:34:21,088| WAR | MainThrea/0954@sshtunnel | Could not read SSH configuration file: ~/.ssh/config
2016-10-06 12:34:21,153| INF | MainThrea/0981@sshtunnel | 0 keys loaded from agent
2016-10-06 12:34:21,963| DEB | MainThrea/1160@sshtunnel | Private key file (/etc/ssh/lavenham_private_key.key, <class 'paramiko.rsakey.RSAKey'>) successfully loaded
2016-10-06 12:34:22,003| INF | MainThrea/0901@sshtunnel | Connecting to gateway: lavenham.co.uk:22 as user 'lavenham'
2016-10-06 12:34:22,062| DEB | MainThrea/0904@sshtunnel | Concurrent connections allowed: True
2016-10-06 12:34:22,117| DEB | MainThrea/1300@sshtunnel | Trying to log in with key: b'611711d06f2b671960c3458d25ca3c20'
2016-10-06 12:34:23,083| INF | Srv-39033/1334@sshtunnel | Opening tunnel: 0.0.0.0:39033 <> 127.0.0.1:3306
Checkpoint 1
2016-10-06 12:34:23,290| INF | MainThrea/1350@sshtunnel | Shutting down tunnel ('0.0.0.0', 39033)
2016-10-06 12:34:23,424| INF | Srv-39033/1340@sshtunnel | Tunnel: 0.0.0.0:39033 <> 127.0.0.1:3306 released
2016-10-06 12:34:23,426| DEB | MainThrea/1363@sshtunnel | Transport is closed
Checkpoint 2
Traceback (most recent call last):
  File "/home/pi/Documents/iot_pm2/2016-10-06.py", line 33, in <module>
    SyncActions()
  File "/home/pi/Documents/iot_pm2/2016-10-06.py", line 27, in SyncActions
    remotecur.execute("SELECT ActionID, Description FROM cmAction")
  File "/usr/local/lib/python3.4/dist-packages/pymysql/cursors.py", line 146, in execute
    result = self._query(query)
  File "/usr/local/lib/python3.4/dist-packages/pymysql/cursors.py", line 296, in _query
    conn.query(q)
  File "/usr/local/lib/python3.4/dist-packages/pymysql/connections.py", line 819, in query
    self._affected_rows = self._read_query_result(unbuffered=unbuffered)
  File "/usr/local/lib/python3.4/dist-packages/pymysql/connections.py", line 1001, in _read_query_result
    result.read()
  File "/usr/local/lib/python3.4/dist-packages/pymysql/connections.py", line 1285, in read
    first_packet = self.connection._read_packet()
  File "/usr/local/lib/python3.4/dist-packages/pymysql/connections.py", line 945, in _read_packet
    packet_header = self._read_bytes(4)
  File "/usr/local/lib/python3.4/dist-packages/pymysql/connections.py", line 981, in _read_bytes
    2013, "Lost connection to MySQL server during query")
pymysql.err.OperationalError: (2013, 'Lost connection to MySQL server during query')

Answer 1

As per steven-rumbalski 's comment above:

Replace: with SSHTunnelForwarder(...) as server
With: server = SSHTunnelForwarder(...)
Then wrap: server.start() ... server.stop()
around the code you want to be sent via the SSH Tunnel.

Here is the converted code:

import pymysql, shlex, shutil, subprocess
import logging
import sshtunnel
from sshtunnel import SSHTunnelForwarder
import iot_config as cfg

def OpenSSHTunnel():
    global server
    sshtunnel.DEFAULT_LOGLEVEL = logging.DEBUG
    server = SSHTunnelForwarder(
        (cfg.sshconn['host'], cfg.sshconn['port']),
        ssh_username = cfg.sshconn['user'],
        ssh_private_key = cfg.sshconn['private_key_loc'],
        ssh_private_key_password = cfg.sshconn['private_key_passwd'],
        remote_bind_address = ('127.0.0.1', 3306)
    )

def OpenRemoteDB():
    global remotecur, remotedb
    remotedb = None
    remotedb = pymysql.connect(
        host='127.0.0.1',
        user=cfg.remotedbconn['user'],
        passwd=cfg.remotedbconn['passwd'],
        db=cfg.remotedbconn['db'],
        port=server.local_bind_port
    )
    remotecur = remotedb.cursor()
    print("Checkpoint 1")

def SyncActions():
    print("Checkpoint 2")
    # this should now work as expected
    remotecur.execute("SELECT ActionID, Description FROM cmAction")
    for r in remotecur:
        print(r)

# Main program starts here
OpenSSHTunnel()
server.start()
OpenRemoteDB()
SyncActions()
server.stop()