Let's say you are getting something like this.

I got this after creating my first backstage app on an Amazon Web Services (AWS) EC2 Linux instance. Check out my article Install Backstage on Linux.

In my web browser I opened the F12 developer console and saw "failed to load resource" with a reference to localhost on port 7007.

This will definitely be returned if the backstage backend is not running. By default, the backend listens for connections on port 7007 so you can use netstat to determine if the backend is listening for connections on port 7007.

~]# netstat -anop | grep 7007
tcp6       0      0 :::7007                 :::*                    LISTEN      6494/node            off (0.00/0/0)

Check out my article Starting backstage using yarn for instructions on how to start the Backstage frontend and backend.

You will also want to ensure that the baseUrl, host, port and origin in app-config.yaml are correct. 

app:
  title: Scaffolded Backstage App
  baseUrl: http://35.173.134.102:3000
  listen:
    host: 0.0.0.0
    
backend:
  baseUrl: http://35.173.134.102:7007
  listen:
    port: 7007
  cors:
    origin: http://35.173.134.102:3000