Flask web app not responding to external requests on EC2 - python-2.7

Question

I've got a very simple Flask application that I'm hosting on an Amazon EC2 node and for whatever reason I can't see it externally. The flask app is here
from flask import Flask
app = Flask(__name__)
app.config['DEBUG'] = False
#app.route('/')
def hello_world():
return 'Hello World!'
#app.route('/p1')
def p1():
return "P1!!!"
if __name__ == '__main__':
app.run(host='0.0.0.0')
When I run the script it looks like the server is running fine, so in my browser (on a different computer) I put the following :5000 (the IP address I pull off of AWS). What's interesting is that it just seems to hang, and eventually produces an error. My guess is that I'm missing some configuration in AWS but I don't know what it is. Any help would be greatly appreciated
EDIT I tried deploying the app on my local machine. And when I try to access it from the browser using localhost:5000, it works. When I replace localhost with my IP address, it fails

Answer 1

Found this question while searching for a solution to the same issue.
edit run.py to enable flask to respond to requests from other than localhost.
this example enables responding to requests from anywhere. good security policies would use something more restrictive.
app.run(host='0.0.0.0')
in the AWS control panel go to EC2: select instance.
the browser should be pointed to the address from 'Public DNS (IPv4)'
(the ip# from IPv4 Public IP might also be useful)
look for 'Security groups': right-click to open the security group on a new page.
check inbound rules.
by default, flask binds to port 5000. add rule permitting incoming TCP traffic on port 5000.
while good security protocol should limit the number of ports left open and the range of IP's permitted to connect, it might be easier to permit 'anywhere' to connect over 'all tcp'.
NB: check if the default port has been changed in the flask config file run.py
ie: line below changes port from the default 5000 to 3000.
app.run(debug=True, port=3000)
Can also check if the flask instance is working locally by ssh'ing to the server and using a local instance of the lynx text browser to verify the port is responding. ie
lynx localhost:5000

Answer 2

Was able to ultimately answer my own question, both really
The problem I was having on AWS was that my inbound for that EC2 was not allowing access through the ports that I would need.
When I tried running it on my local machine at work, firewall settings change the address of localhost (and my IP) so that's why I couldn't access it outside of using localhost:5000

Answer 3

In your EC2 instance, the security group is what restricting your entry to the website.
Go to AWS portal, select your instance
Locate the security group and click the name
in the inbound rule window, select add rule
Not a recommended security practice but to get it running, select All TCP
add '0.0.0.0' in the source
your website will be running

Answer 4

I faced a similar issue in which the Flask app on EC2 instance was not responding. Turns out that I had to modify the inbound rules because:
The default security groups and newly created security groups include default rules that do not enable you to access your instance from the internet.
In order to modify the inbound rules, go to:
Instances dashboard > Security > Security Groups (go to your security group) > Edit Inbound Rules > Add Rule.
Fill the values:
Type -> Custom TCP
Protocol -> TCP
Port range -> 5000 (If your flask app is running on default port)
Source -> Your IP or 0.0.0.0/0 if you want to allow all traffic. You can also select My IP from source dropdown. This will automatically get your IP.
Save and you are good to go!

Answer 5

As you are already using host="0.0.0.0" in your app it should be accessible from anywhere. The only think blocking it is your aws security group inbound rules. Add a All TCP inbound rule for port 0-65535 (your app port should be in this range) with source 0.0.0.0/0 and it should work.