Can't Access Web (Flask) Application from Google Cloud Platform's VM SSH Link - docker-compose

Question

My goal is to run a docker-compose cluster on a VM from Google Cloud Platform. I have successfully installed docker and docker-compose:
$ uname -a
Linux instance-6 4.15.0-1083-gcp #94~16.04.1-Ubuntu SMP Sat Sep 5 22:53:03 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
$ docker -v
Docker version 19.03.13, build 4484c46d9d
$ docker-compose -v
docker-compose version 1.27.3, build 4092ae5d
I am following the basic tutorial to create a docker-compose cluster using: https://docs.docker.com/compose/gettingstarted/ (Steps #1-#4).
My app.py file is:
import time
import redis
from flask import Flask
app = Flask(__name__)
cache = redis.Redis(host='redis', port=6379)
def get_hit_count():
retries = 5
while True:
try:
return cache.incr('hits')
except redis.exceptions.ConnectionError as exc:
if retries == 0:
raise exc
retries -= 1
time.sleep(0.5)
#app.route('/')
def hello():
count = get_hit_count()
return 'Hello World! I have been seen {} times.\n'.format(count)
My requirements.txt file is:
flask
redis
My Dockerfile is:
FROM python:3.7-alpine
WORKDIR /code
ENV FLASK_APP app.py
ENV FLASK_RUN_HOST 0.0.0.0
RUN apk add --no-cache gcc musl-dev linux-headers
COPY requirements.txt requirements.txt
RUN pip install -r requirements.txt
EXPOSE 5000
COPY . .
CMD ["flask", "run"]
And, my docker-compose.yml is:
version: '3'
services:
web:
build: .
ports:
- "5000:5000"
redis:
image: "redis:alpine"
Running docker-compose up gives me the correct output. One of the outputs points to where the web_1 is running.
$ docker-compose up
...
web_1 | * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
...
After pressing the link http://0.0.0.0:5000/, GCP doesn't connect. It tries to go to the URL: https://ssh.cloud.google.com/devshell/proxy?authuser=2&devshellProxyPath=%2F&port=5000&environment_name&environment_id, but then it gives the error: 500. That’s an error. There was an error. Please try again later. That’s all we know.
Going to the external IP address and putting in port 5000 also doesn't return anything. (http://IPAddress:500)
I checked the ports:
$ sudo docker-compose ps
Name Command State Ports
composetest_redis_1 docker-entrypoint.sh redis ... Up 6379/tcp
composetest_web_1 flask run Up 0.0.0.0:5000->5000/tcp
I'm not sure what the reason it. I'm guessing it is the firewall configuration from GCP. Everything is just the default settings. I also allowed HTTP and HTTPS requests in the Compute Engine VM Instance settings. Would really appreciate more guidance on what to do. Thanks in advance!
See below for full output:
$ sudo docker-compose up
Starting composetest_redis_1 ... done
Starting composetest_web_1 ... done
Attaching to composetest_redis_1, composetest_web_1
redis_1 | 1:C 23 Sep 2020 21:40:27.816 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
redis_1 | 1:C 23 Sep 2020 21:40:27.816 # Redis version=6.0.8, bits=64, commit=00000000, modified=0, pid=1, just started
redis_1 | 1:C 23 Sep 2020 21:40:27.816 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf
redis_1 | 1:M 23 Sep 2020 21:40:27.818 * Running mode=standalone, port=6379.
redis_1 | 1:M 23 Sep 2020 21:40:27.818 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
redis_1 | 1:M 23 Sep 2020 21:40:27.818 # Server initialized
redis_1 | 1:M 23 Sep 2020 21:40:27.818 # WARNING overcommit_memory is set to 0! Background save may fail under low memory condition. To fix this issue add 'vm.overcommit_memory = 1' to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit_memory=1' for this to take effect.
redis_1 | 1:M 23 Sep 2020 21:40:27.819 * Loading RDB produced by version 6.0.8
redis_1 | 1:M 23 Sep 2020 21:40:27.819 * RDB age 27 seconds
redis_1 | 1:M 23 Sep 2020 21:40:27.819 * RDB memory usage when created 0.77 Mb
redis_1 | 1:M 23 Sep 2020 21:40:27.819 * DB loaded from disk: 0.000 seconds
redis_1 | 1:M 23 Sep 2020 21:40:27.819 * Ready to accept connections
web_1 | * Serving Flask app "app.py"
web_1 | * Environment: production
web_1 | WARNING: This is a development server. Do not use it in a production deployment.
web_1 | Use a production WSGI server instead.
web_1 | * Debug mode: off
web_1 | * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)

Answer 1

Need to properly allow traffic through that port by:
Creating a firewall rule with a tag
Including that tag in the VM's Network settings
Link here: Network Tags