What do I use for host: in a postgres database when postgres is installed in a google instance?

I have a google cloud intance and in that instance I have dockerize my server and installed postgres (postgres is not dockerized). My goal is to make them talk to each other. I’m having a hard time trying to communicate with one another).
This is how i have my dockerize server is talking to my database:
if i was running this on my local machine i would use host:localhost
I’m not sure what to use for host in a VM ?

const Pool = require('pg').Pool;

const pool = new Pool({
  user: "postgres",
  password: "somepassowed",
  host: '',
  port: 5432,
  database: "postgres"

module.exports = pool;

Source: Docker Questions