Why can't I change the host and port that my Flask app runs on?

The flask command is separate from the flask.run method. It doesn't see the app or its configuration. To change the host and port, pass them as options to the command.

flask run -h localhost -p 3000

Pass --help for the full list of options.

Setting the SERVER_NAME config will not affect the command either, as the command can't see the app's config.

---

Never expose the dev server to the outside (such as binding to 0.0.0.0). Use a production WSGI server such as uWSGI or Gunicorn.

gunicorn -w 2 -b 0.0.0.0:3000 myapp:app

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

if __name__ == '__main__':
    app.run(host="localhost", port=8000, debug=True)

Configure host and port like this in the script and run it with

python app.py

You can also use the environment variable FLASK_RUN_PORT, for instance:

export FLASK_RUN_PORT=8000
flask run
 * Running on http://127.0.0.1:8000/

Source: The Flask docs.