How to get port forwarding working with Jelastic to connect to REPL of running Clojure web app? - portforwarding

Question

I've deployed a simple Clojure web app to Jelastic in a Tomcat container. The Clojure app starts a REPL on port 7001. I have Jelastic SSH Gate set up and working. I SSH into the tomcat node with port forwarding by running this in the terminal on my local machine (where XXX are numbers):
ssh -L 7001:localhost:7001 XXXXX-XXXX#gate.paas.massivegrid.com -p 3022 -N -vv
Then on my local machine I run
lein repl :connect 7001
On the local machine I see:
Connecting to nREPL at 127.0.0.1:7001
ConnectException Connection refused (Connection refused)
On the tomcat node terminal window I see
debug1: Connection to port 7001 forwarding to localhost port 7001 requested.
debug2: fd 10 setting TCP_NODELAY
debug1: channel 2: new [direct-tcpip]
channel 2: open failed: connect failed: Connection refused
debug2: channel 2: zombie
debug2: channel 2: garbage collecting
debug1: channel 2: free: direct-tcpip: listening port 7001 for localhost port 7001, connect from 127.0.0.1 port 57311 to 127.0.0.1 port 7001, nchannels 3
What am I doing wrong? Is this something to do with the way that Jelastic manages ports?
=====================
EDIT: Actually port forwarding works fine
The problem was with the app.
For reference, here's how to check that port forwarding is working on Jelastic. The Jelastic node doesn't have netcat installed so you can't just run netcat -l 7001. However, it does have perl installed, so you can write a perl script to create a listener socket and then run that script on the Jelastic server:
(EDIT 2019_04_06: Instead of using perl script below, just use python -m SimpleHTTPServer 7001 - see comments)
use IO::Socket::INET;
# auto-flush on socket
$| = 1;
# creating a listening socket
my $socket = new IO::Socket::INET (
LocalHost => '0.0.0.0',
LocalPort => '7001',
Proto => 'tcp',
Listen => 5,
Reuse => 1
);
die "cannot create socket $!\n" unless $socket;
print "server waiting for client connection on port 7777\n";
while(1)
{
# waiting for a new client connection
my $client_socket = $socket->accept();
# get information about a newly connected client
my $client_address = $client_socket->peerhost();
my $client_port = $client_socket->peerport();
print "connection from $client_address:$client_port\n";
# read up to 1024 characters from the connected client
my $data = "";
$client_socket->recv($data, 1024);
print "received data: $data\n";
# write response data to the connected client
$data = "ok";
$client_socket->send($data);
# notify client that response has been sent
shutdown($client_socket, 1);
}
$socket->close();
(script from here).
Use nano to write the above into a script listener.pl on the Jelastic node then run perl listener.pl on that node.
On your local machine run
ssh -L 7001:localhost:7001 XXXXX-XXXX#gate.paas.massivegrid.com -p 3022
Then on local machine try curl localhost:7001 and in the terminal for the Jelastic node you should see something like
received data: GET / HTTP/1.1
Host: localhost:7777
User-Agent: curl/7.54.0
Accept: */*