How do I access a remote aws lightsail mongodb over ssh tunnel - mongodb

Question

I have a Lightsail AWS instance up and running with a MEAN stack. I have an existing MEAN stack running on a different network. At the moment the node server.js connects to localhost for the mongo bit (on same machine) and all I want to do is replace the localhost with a connection to my mongo running on my AWS remote server.
I understand, that for security reasons, it is best to ssh tunnel this connection, which I think I am familiar with.
What I have done so far is this:
In a console on the machine hosting the node server (remote to the db) I have run:
ssh -L 8181:127.0.0.1:80 -i ~/LightsailDefaultPrivateKey-eu-west-2.pem bitnami#31.16.56.125 -N
I can then browse to the RockMongo UI from the local machine using localhost:8181/rockmongo ...yay.
If I then run the following:
ssh -L 8181:127.0.0.1:27017 -i ~/LightsailDefaultPrivateKey-eu-west-2.pem bitnami#31.16.56.125 -N
(27017 being the mongo port)
Then try and access the db from my remote machine using:
mongo --username XXXXXX --password XXXXXX 31.16.56.125:8181/testdata
I get the following error:
~]
2017-12-28T22:11:09.791+0000 Error: couldn't connect to server 31.16.56.125:8181 (31.16.56.125), connection attempt failed at src/mongo/shell/mongo.js:148
exception: connect failed
Am I doing this wrong? i.e. is the tunnel only for http connections and not mongo command line use? Do I need to test the connection some other way?
I've Googled all over the place for this and not had much luck (a lot of the AWS docs suggest punching a hole in the firewall - which one can no longer do!)

Answer 1

OK I've (partially) solved this, there were a few things wrong.
1) The mongo client was 2.6 and mongo running on AWS was 3.4. Upgrading this solved some issues - in that I was getting a more meaningful error message.
One thing I did have trouble with is that apt-get seemed to perform an update, yet the version reported when issuing the mongo command was still 2.6.
To solve this I had to run sudo apt-get purge mongodb-org* (note the asterisk). Then perform the update.... If you need to do this then follow these instructions:
https://docs.mongodb.com/v3.2/tutorial/install-mongodb-on-ubuntu/
2) This command
mongo --username XXXXXX --password XXXXXX 31.16.56.125:8181/testdata
won't work as I've omitted 'admin' from it and not specified localhost!
but
mongo admin --username XXXXXX --password XXXXXX localhost:8181/testdata
doesn't work either and gives the following output.
2018-01-03T22:00:42.380+0000 W NETWORK [thread1] Failed to connect to 127.0.0.1:27017, in(checking socket for error after poll), reason: errno:111 Connection refused
2018-01-03T22:00:42.380+0000 E QUERY [thread1] Error: couldn't connect to server 127.0.0.1:27017, connection attempt failed :
connect#src/mongo/shell/mongo.js:229:14
#(connect):1:6
The only command I could get to work is:
mongo admin --username XXXXXX --password XXXXXX --port 8181
The default host is localhost, so in this case it uses the tunnel, this will also just connect to the test db, you can then admin from there.
What I haven't got to the bottom of is the specification of the host:port/db as an argument as per the output from running mongo --help
usage: mongo [options] [db address] [file names (ending in .js)]
db address can be:
foo foo database on local machine
192.169.0.5/foo foo database on 192.168.0.5 machine
192.169.0.5:9999/foo foo database on 192.168.0.5 machine on port 9999