Socket.io 404 on nginx - node.js

Question

So I have been looking through a lot of posts, websites, and have still not gotten this problem fixed.
I have previously had a project running on my server, including socket.io, without problems.
But now that I am uploading this new project to the server, it seems that the socket.io always returns 404.
Sorry if I have overlooked something obvious here.
Nginx config:
server {
listen 80 default_server;
listen [::]:80 default_server;
index index.html index.htm index.nginx-debian.html;
server_name localhost;
location / {
proxy_pass http://localhost:3001;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection 'upgrade';
proxy_set_header Host $host;
proxy_cache_bypass $http_upgrade;
}
location /demo/ {
proxy_pass http://localhost:3000/;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection 'upgrade';
proxy_set_header Host $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_cache_bypass $http_upgrade;
}
location /socket.io/ {
proxy_pass http://localhost:3000/;
proxy_redirect off;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-NginX-Proxy true;
proxy_pass_request_headers on;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection 'upgrade';
proxy_set_header Host $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_cache_bypass $http_upgrade;
}
}
My socket.io server:
const app = express();
const server = http.createServer(app);
const io = require('socket.io')(server);
server.listen(3000);
Client (Pug):
script(src="/socket.io/socket.io.js")
Note that the code above is what I have ended up with after reading through a lot of questions on here, on serverfault, aswell as blog posts several places.
I don't remember using a second location "tag" (is that what it is called?) for socket.io for the first one I used.

Answer 1

The proxy pass should be:
location /socket.io/ {
proxy_pass http://localhost:3000/socket.io/;
...
}
Please see https://medium.com/#ibraheemabukaff/how-to-proxy-websockets-with-nginx-e333a5f0c0bb for details...

Answer 2

Giving your Nginx the server name localhost and then trying to proxy_pass to localhost is probably not going to do you any favours.
Try getting rid of the server_name localhost; entirely and changing all these:
proxy_pass http://localhost:xxxx;
to this:
proxy_pass http://127.0.0.1:xxxx;
Or, if you want to do it properly then outside of your server block create an upstream directive:
upstream socketserver {
server 127.0.0.1:3000;
}
and change your proxy_pass directives to:
proxy_pass http://socketserver/;