Socket.io SSL connection with Nginx and Express - node.js

Question

I am trying to use SSL on my application running socket.io with express and nginx but I can't make it work. I have done my research but none of what I found worked.
I keep having the error : ERR_CONNECTION_CLOSED with not http status code on client side.
GET https://subdomain.mywebsite.com:1339/socket.io/?EIO=3&transport=polling&t=LIgxHmz net::ERR_CONNECTION_CLOSED
Here is my nginx configuration :
server {
listen 443;
server_name subdomain.mywebsite.com;
root /usr/share/nginx/html;
index index.html index.htm;
ssl on;
# Use certificate and key provided by Let's Encrypt:
ssl_certificate /etc/letsencrypt/live/subdomain.mywebsite.com/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/subdomain.mywebsite.com/privkey.pem;
ssl_session_timeout 5m;
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
ssl_prefer_server_ciphers on;
ssl_ciphers 'EECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH';
location / {
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_set_header X-NginX-Proxy true;
proxy_pass http://localhost:1339/;
proxy_redirect off;
# Socket.IO Support
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
}
Here is the server side :
var express = require('express'),
var app = express();
var server = require('http').createServer(app);
var io = require('socket.io')(server);
server.listen(1339);
...
Here is the client side :
subdomain.mywebsite.com
var socket = io.connect("https://subdomain.mywebsite.com:1339");
The page loads nicely, no error on server side but no connection to socket.io.
Everything worked flawlessly before I tried to switch to SSL.
What am I doing wrong ?

Answer 1

Try this configuration. Please make sure to have a correct SSL certificate and key. If you test on local you can easily use mkcert tool to generate SSL certificate to local testing.
server {
listen 80;
server_name <your server_name>;
return 301 https://<your server_name>$request_uri;
}
server {
listen 443 ssl;
ssl_certificate <your certificate path>; # better if you put them at /etc/nginx/ssl/
ssl_certificate_key <your certificate_key path >;
server_name <your server_name>;
location / {
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Client-Verify SUCCESS;
proxy_set_header Host $http_host;
proxy_set_header X-NginX-Proxy true;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
proxy_pass http://localhost:3000;
proxy_redirect off;
proxy_buffering off;
}
}