Flask 'Cannot assign requested address' error when binding to a specific IP on Pterodactyl

I have Virtual Dedicated Server based on Ubuntu 20.04.6 with IP address 193.23.xxx.xx. blizcore.fun resolves to this IP. On this server I installed pterodactyl panel. Pterodactyl have IP 172.18.0.0/16. I install basic python 3.10 egg on pterodactyl and create server to port 6668.

My target: create GET request to https://blizcore.fun/status. This request should be handled by the Flask server running within the Pterodactyl environment.

Code:

from flask import Flask, request
from flask_restful import Api, Resource, abort

from dotenv import load_dotenv
load_dotenv()
import os

key = os.getenv("AUTH_KEY")

app = Flask(__name__)
api = Api()

class BlizcoreApi(Resource):
    def get(self):
        headers = request.headers
        auth = headers.get("Authorization")
        if auth == key:
            return {"code": 200, "message": "All working stable."}
        else:
            return abort(401, message="Unauthorized.")
    

api.add_resource(BlizcoreApi, "/status")
api.init_app(app)

if __name__ == "__main__":
    app.run(host="193.23.220.14", port=6668, debug=True)

But i have error (console output of server on port 6668):

 * Serving Flask app 'server'
 * Debug mode: on
Cannot assign requested address

I tried connect flask to host 0.0.0.0 for listen on all interfaces and Im connected to pterodactyl IP (console output after these actions):

* Serving Flask app 'server'
 * Debug mode: on
WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
 * Running on all addresses (0.0.0.0)
 * Running on http://127.0.0.1:6668
 * Running on http://172.18.0.6:6668
Press CTRL+C to quit
 * Restarting with stat
 * Debugger is active!
 * Debugger PIN: 144-915-975

Rules on Firewall looks like that:

root@vm25-lendnodes:~# sudo ufw status
Status: active

To                         Action      From
--                         ------      ----
22                         ALLOW       Anywhere                  
80                         ALLOW       Anywhere                  
443                        ALLOW       Anywhere                  
...
6668                       ALLOW       172.18.0.0/24
...

I think I need to make a router to connect the stream from 172.18.0.6:6668 to 193.23.xxx.xx:6668, but it just my theory.

Solution

I solved my problem, making this actions:

Creating new flask-app on Ubuntu directory /etc/nginx/sites-available and add in this app listener to port 3001 and set location is my server http://172.18.0.6:6668:

server {
    listen [::]:3001 ssl ipv6only=on;
    listen 3001 ssl;
    server_name blizcore.fun;

    ssl_certificate /etc/letsencrypt/live/blizcore.fun/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/blizcore.fun/privkey.pem;

    ssl_protocols TLSv1.2 TLSv1.3;
    ssl_ciphers HIGH:!SSLv3:!aNULL;
    ssl_prefer_server_ciphers on;

    location / {
        proxy_pass http://172.18.0.6:6668;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

Create simlink to flask-app in /etc/nginx/sites-enabled:

sudo ln -s /etc/nginx/sites-available/flask-app /etc/nginx/sites-enabled/

Change Firewall rules for connecting to port 3001 from anybody (dont thing its good idea but this work. For now I dont have big traffic and dont have ddos-attack so I make this just for working Flask server):

root@vm25-lendnodes:~# sudo ufw status
Status: active

To                         Action      From
--                         ------      ----
22                         ALLOW       Anywhere                  
80                         ALLOW       Anywhere                  
443                        ALLOW       Anywhere                  
...                      
3001                       ALLOW       Anywhere                  
22 (v6)                    ALLOW       Anywhere (v6)             
80 (v6)                    ALLOW       Anywhere (v6)             
443 (v6)                   ALLOW       Anywhere (v6)             
...           
3001 (v6)                  ALLOW       Anywhere (v6)

I change host in my Flask app in python file:

if __name__ == "__main__":
    app.run(host="172.18.0.6", port=6668, debug=True)

And now, i can create GET request to https://blizcore.fun:3001/status and my Flask server response on this request looks like what i want:

root@vm25-lendnodes:~# curl https://blizcore.fun:3001/status
{"message": "Unauthorized."}
root@vm25-lendnodes:~# curl https://blizcore.fun:3001/status -H "Authorization: mUoh68Bu3WcwQ5dr4lbo" #if you reading this, please do not abuse it, just test this url for yourself, otherwise I will change the key.
{"code": 200, "message": "All working stable."}