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Editorial Team
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Asked: 2026-06-15T05:28:45+00:00

When a user logs into my sample application I add a username key into

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When a user logs into my sample application I add a username key into the session object and I hang a user object off of the global “g” object. See below.

@app.route('/login/', methods=['GET', 'POST'])
def login():
    """Logs the user in."""

    error = None
    if request.method == 'POST':
        print("login hit")
        user = get_user(request.form['username'])
        if user is None:
            error = 'Invalid username'
            print error
        elif not check_password_hash(user.password, request.form['password']):
            error = 'Invalid password'
            print error
        else:
            flash('You were logged in')
            print "logged in"
            session['username'] = request.form['username']
            g.user = request.form['username']
            print error, "error"
            return redirect(url_for('main'))

Now, if the user logs in successfully (which is what is happening), he will redirect to the main page. This will teardown the old request and spawn a new one. The problem is that when a new request starts the session is wiped. I am printing out the session keys and they are all empty. This only happens on heroku, not on my local machine. What am I doing wrong.

  @app.before_request
    def before_request():
        print session.keys(), session.values()  # shows [] []
        print("before request")
        print ('username' in session, "in session?")
        g.db = connect_db()
        g.user = None
        if "username" in session:
            g.user = get_user(session['username'])
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1 Answer

  1. Editorial Team

    Well, seeing as this indeed would be the answer due to multiple workers I’ll move it from the comments part. 🙂 You don’t want redis at the gunicorn layer, rather in your application. These four links should help you out:

    1) First, enable/install Redis in Heroku

    2) Then check this out (will replace Flasks entire session driver with one based on redis):
    This might be overkill, I’d simply use redis as a key-storage value in the app (check my third link) but you might like this approach.

    3) Not as related but shows some usage examples (queue system for flask with redis)

    4) Basic redis tutorial for python

    These three links should get you started, if it’s not enough I’ll dig up some more examples so just ask if you need them!

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