Getting 502 bad gateway and 400 bad request with flask_socketio + flask + gunicorn + nginx

Question

So I have been setting up a website with flask + flask_socketio + eventlet + gunicorn + nginx. I have looked at the documentation for flask_socketio for this configuration and it is supported. Though after using the website I noticed that while flask would work perfectly, flask_socketio would not work at all. Here are the relevant configuration and error codes. I would like to note that some flask_socketio bits post requests would go through with a 200 OK.
This is on ubuntu 18.04
Nginx:

user www-data;
worker_processes auto;
pid /run/nginx.pid;
include /etc/nginx/modules-enabled/*.conf;

events {
    worker_connections 65535;
    multi_accept on;
}

http {

    ##
    # Basic Settings
    ##
    charset utf-8;
    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    keepalive_timeout 65;
    types_hash_max_size 2048;
    server_tokens off;
    log_not_found off;
    client_max_body_size 16M;
    # server_names_hash_bucket_size 64;
    # server_name_in_redirect off;

    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    ##
    # SSL Settings
    ##

    ssl_protocols TLSv1 TLSv1.1 TLSv1.2; # Dropping SSLv3, ref: POODLE
    ssl_prefer_server_ciphers on;

    ##
    # Logging Settings
    ##

    access_log /var/log/nginx/access.log;
    error_log /var/log/nginx/error.log;

    ##
    # Gzip Settings
    ##

    gzip on;

    # gzip_vary on;
    # gzip_proxied any;
    # gzip_comp_level 6;
    # gzip_buffers 16 8k;
    # gzip_http_version 1.1;
    # gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;

    ##
    # Virtual Host Configs
    ##
server {
    listen 80;
    server_name http://compoundingly.com;

    location / {
        proxy_pass http://0.0.0.0:5000;
    proxy_redirect off;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }
    location /static {
        alias /home/shorya/compoundingly_website/compoundingly_code/static;
        expires 30d;
    }
    location /socket.io {
        include proxy_params;
        proxy_http_version 1.1;
        proxy_buffering off;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
        proxy_pass http://0.0.0.0:5000/socket.io;
    }
}

    include /etc/nginx/conf.d/*.conf;
    include /etc/nginx/sites-enabled/*;
}

Gunicorn service

[Unit]
Description=Gunicorn instance to serve myproject
Requires=gunicorn.socket
After=network.target

[Service]
User=root
Group=www-data
WorkingDirectory=/home/shorya/compoundingly_website/compoundingly_code
Environment="PATH=/home/shorya/compoundingly_website/compoundingly_code/compoundingly_venv/bin"
ExecStart=/home/shorya/compoundingly_website/compoundingly_code/compoundingly_venv/bin/gunicorn -k eventlet --workers 3 --bind unix:compoundingly_code.sock -m 007 wsgi:app
Restart=on-failure
[Install]
WantedBy=multi-user.target

wsgi.py

from app import app

if __name__ == "__main__":
    app.run()

pip3 freeze

click==7.1.2
dnspython==1.16.0
eventlet==0.26.1
Flask==1.1.2
Flask-SocketIO==4.3.1
greenlet==0.4.16
gunicorn==19.7.1
itsdangerous==1.1.0
Jinja2==2.11.2
MarkupSafe==1.1.1
monotonic==1.5
pkg-resources==0.0.0
python-engineio==3.13.1
python-socketio==4.6.0
six==1.15.0
Werkzeug==1.0.1

failed request

URL: http://compoundingly.com/socket.io/?EIO=3&transport=polling&t=NFGwVcP&sid=22ad9ddeaffe4eeb8525927aca86806b
Status: 400 BAD REQUEST
Source: Network
Address: 192.241.149.99:80
Initiator: 
index.js:83

good request

URL: http://compoundingly.com/socket.io/?EIO=3&transport=polling&t=NFGwVtd
Status: 200 OK
Source: Network
Address: 192.241.149.99:80
Initiator: 
index.js:83

502 bad gateway request

URL: http://compoundingly.com/socket.io/?EIO=3&transport=polling&t=NFGwdji&sid=69f16b45a1aa474294cdeb2452f0e71a
Status: 502 Bad Gateway
Source: Network
Address: 192.241.149.99:80
Initiator: 
index.js:83

Gunicorn error log

Aug 08 22:09:16 sm01 gunicorn[1956]: [2020-08-08 22:09:16 -0400] [5964] [INFO] Booting worker with pid: 5964
Aug 08 22:09:47 sm01 gunicorn[1956]: [2020-08-08 22:09:47 -0400] [1956] [CRITICAL] WORKER TIMEOUT (pid:5962)
Aug 08 22:09:47 sm01 gunicorn[1956]: [2020-08-08 22:09:47 -0400] [5962] [INFO] Worker exiting (pid: 5962)
Aug 08 22:09:47 sm01 gunicorn[1956]: [2020-08-08 22:09:47 -0400] [5977] [INFO] Booting worker with pid: 5977
Aug 08 22:09:48 sm01 gunicorn[1956]: [2020-08-08 22:09:48 -0400] [1956] [CRITICAL] WORKER TIMEOUT (pid:5963)
Aug 08 22:09:48 sm01 gunicorn[1956]: [2020-08-08 22:09:48 -0400] [1956] [CRITICAL] WORKER TIMEOUT (pid:5964)
Aug 08 22:09:48 sm01 gunicorn[1956]: [2020-08-08 22:09:48 -0400] [5963] [INFO] Worker exiting (pid: 5963)
Aug 08 22:09:48 sm01 gunicorn[1956]: [2020-08-08 22:09:48 -0400] [5964] [INFO] Worker exiting (pid: 5964)
Aug 08 22:09:48 sm01 gunicorn[1956]: [2020-08-08 22:09:48 -0400] [5981] [INFO] Booting worker with pid: 5981
Aug 08 22:09:48 sm01 gunicorn[1956]: [2020-08-08 22:09:48 -0400] [5982] [INFO] Booting worker with pid: 5982

For people who are facing this same problem there are a few things you can do to make the system work after you have done this: I changed my wsgi to:

from app import *

if __name__ == "__main__":
    #app.run()
    app = Flask(__name__)#,template_folder="./dist/app/templates"
    app.config['SECRET_KEY'] = 'secret!'
    socketio = SocketIO(app,async_mode="eventlet")
    socketio.run(app,host="0.0.0.0",port=5000,debug=True)

added --bind 0.0.0.0:5000 to the gunicorn command.
I also downloaded a newer version of gunicorn but not the newest.
19.7 does not work
20.0.3 works
20.0.4 does not work

Answer 1

See the documentation for how to run Gunicorn with eventlet. In particular, you are using multiple workers, which is not supported.

Example supported configuration from the docs:

gunicorn --worker-class eventlet -w 1 module:app