Socket.io is working on Local Host but not Heroku - node.js

Question

I managed to get sockets to work on my LocalHost, however when uploading to Heroku I get the following errors.
Heroku logs:
2020-02-26T19:18:12.223451+00:00 heroku[router]: at=info method=GET path="/socket.io/?EIO=3&transport=polling&t=N22xsN8" host=evening-beach-84352.herokuapp.com request_id=9e085385-d06d-42f8-a02b-741ebdb50139 fwd="99.239.140.92" dyno=web.1 connect=1ms service=7ms status=200 bytes=1156 protocol=https
2020-02-26T19:18:16.268249+00:00 heroku[router]: at=info method=GET path="/socket.io/?EIO=3&transport=polling&t=N22xtMN" host=evening-beach-84352.herokuapp.com request_id=560a1283-e9ad-4f98-b65d-c98e3af0d989 fwd="99.239.140.92" dyno=web.1 connect=1ms service=7ms status=200 bytes=1156 protocol=https
2020-02-26T19:18:16.340518+00:00 heroku[router]: at=info method=POST path="/socket.io/?EIO=3&transport=polling&t=N22xtNI" host=evening-beach-84352.herokuapp.com request_id=0747c99f-bfa7-4a48-9dc9-396237ea4afd fwd="99.239.140.92" dyno=web.1 connect=1ms service=17ms status=404 bytes=417 protocol=https
2020-02-26T19:18:16.345722+00:00 heroku[router]: at=info method=GET path="/socket.io/?EIO=3&transport=polling&t=N22xtNd" host=evening-beach-84352.herokuapp.com request_id=c28aa30e-c33f-4d2b-809d-7f723c9ad2f8 fwd="99.239.140.92" dyno=web.1 connect=1ms service=11ms status=200 bytes=1156 protocol=https
2020-02-26T19:18:16.394512+00:00 heroku[router]: at=info method=POST path="/socket.io/?EIO=3&transport=polling&t=N22xtOS" host=evening-beach-84352.herokuapp.com request_id=93635a58-6c21-4d1a-81b4-ba67c712bc4a fwd="99.239.140.92" dyno=web.1 connect=1ms service=3ms status=404 bytes=417 protocol=https
2020-02-26T19:18:18.146871+00:00 heroku[router]: at=info method=GET path="/socket.io/?EIO=3&transport=polling&t=N22xtpq" host=evening-beach-84352.herokuapp.com request_id=8dc8077a-5719-4f97-bd60-dc2f9585efea fwd="99.239.140.92" dyno=web.1 connect=1ms service=5ms status=200 bytes=1156 protocol=https
2020-02-26T19:18:18.104971+00:00 heroku[router]: at=info method=GET path="/socket.io/?EIO=3&transport=polling&t=N22xtp6" host=evening-beach-84352.herokuapp.com request_id=1a135498-5911-4757-90a6-52f22188b3ae fwd="99.239.140.92" dyno=web.1 connect=1ms service=8ms status=200 bytes=1156 protocol=https
2020-02-26T19:18:18.174618+00:00 heroku[router]: at=info method=POST path="/socket.io/?EIO=3&transport=polling&t=N22xtqB" host=evening-beach-84352.herokuapp.com request_id=dce824bb-5243-45be-bd9b-5be3026412ac fwd="99.239.140.92" dyno=web.1 connect=1ms service=3ms status=404 bytes=417 protocol=https
2020-02-26T19:18:18.235090+00:00 heroku[router]: at=info method=POST path="/socket.io/?EIO=3&transport=polling&t=N22xtr2" host=evening-beach-84352.herokuapp.com request_id=44dbc61d-5e40-4283-b602-77107c20bdcd fwd="99.239.140.92" dyno=web.1 connect=1ms service=7ms status=404 bytes=417 protocol=https
Browser console logs:
polling-xhr.js:271 POST https://evening-beach-84352.herokuapp.com/socket.io/?EIO=3&transport=polling&t=N22yWHd 404 (Not Found)
I have this set up on my client side code:
import socketIOClient from "socket.io-client";
const socket = socketIOClient("https://evening-beach-84352.herokuapp.com/")
And this one my server side code:
const server = require('http').Server(app);
const socketIO = require('socket.io')
const io = socketIO(server, { origin: "*:*" });
const PORT = process.env.PORT || 8080;

Answer 1

Have you enabled session affinity in your app? From the support article:
Apps using Socket.io should enable session affinity. If you plan to
use Node’s Cluster module or to scale your app to multiple dynos, you
should also follow Socket.io’s multiple-nodes instructions.
heroku features:enable http-session-affinity

Answer 2

I just started using Heroku recently and just added socket.io to my application and am seeing similar errors. Yesterday they went away, today they are back. I have two tabs in my browser 1 works the other doesn't...
The difference: http vs https
When you click the link in Heroku to take you to your app it navigates to https://myapp.herokuapp.com but if I manually navigate to http://myapp.herokuapp.com suddenly all the errors go away.
Now I'd like to know the reason why one works and the other doesn't...