Web application using Python3 not working when Dockerized - python-3.x

Question

HelloWorld-1.py
app = Flask(__name__)
#app.route('/')
def printHelloWorld():
print("+++++++++++++++++++++")
print("+ HELLO WORLD-1 +")
print("+++++++++++++++++++++")
return '<h1>Bishwajit</h1>'
# return '<h1>Hello %s!<h1>' %name
if name == '__main__':
app.run(debug='true')
Dockerfile
FROM python:3
ADD HelloWorld-1.py /HelloWorld-1.py
RUN pip install flask
EXPOSE 80
CMD [ "python", "/HelloWorld-1.py"]
Building docker using the below command
docker build -t helloworld .
Running docker image using below command
docker run -d --name helloworld -p 80:80 helloworld
when i run the below command
docker ps -a
i get the below output
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
cebfe8a22493 helloworld "python /home/HelloW…" 2 minutes ago Up 2 minutes (unhealthy) 0.0.0.0:80->80/tcp helloworld
If I hit in the browser(127.0.0.1:5000), it does not give response,
But when i run the python file individually, it runs properly in the browser.

Answer 1

I reproduced your problem and there were four main problems:
Not importing flask.
Using name instead of __name__
Not assigning the correct port.
Not assigning the host.
This is how your HelloWorld-1.py should look like:
from flask import Flask
app = Flask(__name__)
#app.route('/')
def printHelloWorld():
print("+++++++++++++++++++++")
print("+ HELLO WORLD-1 +")
print("+++++++++++++++++++++")
return '<h1>Bishwajit</h1>'
# return '<h1>Hello %s!<h1>' %name
if __name__ == '__main__':
app.run(host='0.0.0.0')
This is how you Dockerfile should look like:
FROM python:3
ADD HelloWorld-1.py .
RUN pip install flask
CMD [ "python", "/HelloWorld-1.py"]
Then simply build and run:
docker build . -t helloflask
docker run -dit -p 5000:5000 helloflask
Now go to localhost:5000 and it should work.
Additionally: You could actually assign any other port, for example 4444, and then go to localhost:4444:
docker run -dit -p 4444:5000 helloflask