Compute Engine : "This site can’t be reached" - node.js

Question

SITUATION:
I am following this tutorial.
When I get to the part where I create an instance and I execute the necessary commands, I get to the following:
To see the application running, go to http://[YOUR_INSTANCE_IP]:8080,
where [YOUR_INSTANCE_IP] is the external IP address of your instance.
PROBLEM:
The page deosn't load. I get the following error message:
This site can’t be reached
QUESTION:
What could have gone wrong ?
All previous steps worked perfectly and I was able to access my website locally.
I waited for the Compute Engine instance to be ready by checking:
gcloud compute instances get-serial-port-output my-app-instance --zone us-central1-f
and although I reproduced all the steps twice, I am still met with the error message.
Something must be missing.
EDIT:
My firewall rules:

Answer 1

I guess you don't apply firewall tag to instance ?
First, you can check your compute instences tags.
gcloud compute instances describe my-app-instance
In your example , you should see http-server in tags-items, like follows
tags:
fingerprint: xxxxxxx
items:
- http-server
- https-server
If not exist, you should add the tags to an existing VM instance, use this gcloud command:
gcloud compute instances add-tags [YOUR_INSTANCE_NAME] --tags http-server,https-server
To add the tags at the time of the instance creation, include that flag in your statement:
gcloud compute instances create [YOUR_INSTANCE_NAME] --tags http-server,https-server

Answer 2

If your code and firewall rules are correct then it's highly possible that you are trying to connect to wrong IP. You should be using external IP, not internal one which you get using ifconfig, you can get your external IP at whatsmyip.com

Answer 3

I will suggest looking into this step:
gcloud compute instances create my-app-instance \
--image-family=debian-9 \
--image-project=debian-cloud \
--machine-type=g1-small \
--scopes userinfo-email,cloud-platform \
--metadata app-location=$BOOKSHELF_DEPLOY_LOCATION \
--metadata-from-file startup-script=gce/startup-script.sh \
--zone us-central1-f \
--tags http-server
Please ensure the instance is created with the http-server tag
Otherwise, the firewall rules will not take effect on your instance
gcloud compute firewall-rules create default-allow-http-8080 \
--allow tcp:8080 \
--source-ranges 0.0.0.0/0 \
--target-tags http-server \
--description "Allow port 8080 access to http-server"

Answer 4

First, check if the firewall settings are correct as the others had mentioned.
Second, I was having the same problem and solve it by selecting on the Network Service Tier section the "Standard" option instead of the "Premium" one.
Third, check if there is another application running on the same port using the command:
netstat -tulpn
Which should return something like:
(Not all processes could be identified, non-owned process info
will not be shown, you would have to be root to see it all.)
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN -
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN -
tcp6 0 0 :::80 :::* LISTEN -
In my case it was not working because I had two applications running on the same port.