Python flask dual-stack on WINDOWS (ipv4 and ipv6)

According to [PalletProjects.Flask]: run(host=None, port=None, debug=None, load_dotenv=True, **options):

Do not use run() in a production setting. It is not intended to meet security and performance requirements for a production server. Instead, see Deployment Options for WSGI server recommendations.

NGINX knows how to handle this exact scenario.

In development mode, I don't know why is so important to listen on all addresses, as things can be tested listening on one at a time.

I didn't see any easy way of making this work. As a note, on Lnx things seem to be easier as the IPv4-mapped IPv6 addresses are controlled via the net.ipv6.bindv6onl setting.

There are however a number of ways to work things around, here's one that executes the current file (itself) in a new process for each listening IP address (and does it in a thread, since the (child) process blocks the execution).

code00.py:

#!/usr/bin/env python3import sysfrom flask import Flaskimport threadingimport subprocessapp = Flask(__name__)def run_flask(host):    return subprocess.call([sys.executable, sys.argv[0], host])@app.route("/")def hello_world():    return "Hello World! <strong>I am learning Flask</strong>", 200def main(argv):    port = 5000    debug = True    if argv:        app.run(host=argv[0], port=port, debug=debug)    else:        hosts = [            "127.0.0.1",            "::1",        ]        threads = list()        for host in hosts:            threads.append(threading.Thread(target=run_flask, args=(host,)))        for idx, thread in enumerate(threads):            print("Starting on {0:s}:{1:d}".format(hosts[idx], port))            thread.start()if __name__ == "__main__":    print("Python {0:s} {1:d}bit on {2:s}\n".format(" ".join(item.strip() for item in sys.version.split("\n")), 64 if sys.maxsize > 0x100000000 else 32, sys.platform))    main(sys.argv[1:])    print("\nDone.")

Output (it's a bit mixed):

[cfati@CFATI-5510-0:e:\Work\Dev\StackOverflow\q057881991]> "e:\Work\Dev\VEnvs\py_064_03.07.03_test0\Scripts\python.exe" code00.pyPython 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)] 64bit on win32Starting on 127.0.0.1:5000Starting on ::1:5000Done.Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)] 64bit on win32Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)] 64bit on win32 * Serving Flask app "code00" (lazy loading) * Serving Flask app "code00" (lazy loading) * Environment: production * Environment: production   WARNING: Do not use the development server in a production environment.   WARNING: Do not use the development server in a production environment.   Use a production WSGI server instead. * Debug mode: on   Use a production WSGI server instead. * Debug mode: on * Restarting with stat * Restarting with statPython 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)] 64bit on win32Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)] 64bit on win32 * Debugger is active! * Debugger is active! * Debugger PIN: 566-002-078 * Debugger PIN: 566-002-078 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit) * Running on http://[::1]:5000/ (Press CTRL+C to quit)

As seen, the servers start listening on the given addresses (you can remove the print calls, in order to have less output). Also (on another cmd):

[cfati@CFATI-5510-0:C:\WINDOWS\system32]> netstat -an | findstr 5000  TCP    127.0.0.1:5000         0.0.0.0:0              LISTENING  TCP    [::1]:5000             [::]:0                 LISTENING

You could also operate at OS level, by playing with the /etc/hosts file, but I didn't test that.