Cannot remote connect to gremlin server from express (Node.js) - node.js

Question

I have set up a Janusgraph Docker instance (janusgraph/janusgraph:latest - Lucene/BerkeleyDB/Tinkerpop/Gremlin Server) in a Linux VM in my datacentre. On the same VM and on my laptop, I've run the same JanusGraph Docker image but run the gremlin console (adjusting conf/remote.yaml to point to the gremlin server) and successfully imported air-routes.graphml into the server instance. I can also successfully query the air-routes data with some simple traversals.
In summary: I'm confident that the server is running, has data, can be remotely connected and respond to traversals.
I have been stuck on the next step for a long, long time:
I have created a basic Node express stub:
var createError = require('http-errors');
var express = require('express');
var path = require('path');
var cookieParser = require('cookie-parser');
var logger = require('morgan');
var gremlin = require('gremlin');
const DriverRemoteConnection = gremlin.driver.DriverRemoteConnection;
const traversal = gremlin.process.AnonymousTraversalSource.traversal;
var indexRouter = require('./routes/index');
var usersRouter = require('./routes/users');
var app = express();
// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'pug');
app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));
app.use('/', indexRouter);
app.use('/users', usersRouter);
// catch 404 and forward to error handler
app.use(function(req, res, next) {
next(createError(404));
});
// error handler
app.use(function(err, req, res, next) {
// set locals, only providing error in development
res.locals.message = err.message;
res.locals.error = req.app.get('env') === 'development' ? err : {};
// render the error page
res.status(err.status || 500);
res.render('error');
});
module.exports = app;
const g = traversal().withRemote(
new DriverRemoteConnection('ws://mygremlinserverhost:8182/gremlin'));
This fails with the following:
npm run start
greg:air-routes/ $ npm run start [21:07:39]
Debugger attached.
> air-routes#0.0.0 start
> node ./bin/www
Debugger attached.
Waiting for the debugger to disconnect...
node:internal/process/promises:227
triggerUncaughtException(err, true /* fromPromise */);
^
Error: connect ECONNREFUSED <The IP of the VM>:8182
at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1138:16) {
errno: -61,
code: 'ECONNREFUSED',
syscall: 'connect',
address: '<The IP of the VM>',
port: 8182
}
Waiting for the debugger to disconnect...
greg:air-routes/ $
(Also, I don't understand this notification, or whether it's the cause (or effect) of the inability to connect - What am I doing wrong or not doing. Please assume an idiot novice who needs the basics explaining. Thanks, I think? ;o) )
node:internal/process/promises:227
triggerUncaughtException(err, true /* fromPromise */);
^

Answer 1

I believe the inability to connect was because I had not specified a docker port mapping to the OS port on the server's docker run command.
Should have been (with the port mapping switch -p)
docker run --name janusgraph-default -p 8182:8182 --volume /myLocalDir/gremlin:/dataImports janusgraph/janusgraph:latest