You should find out the container name of your postgres container. Did you install Odoo and Postgres with docker-compose? Then you should find the container name you should use in this file:

services:

  postgres:
    image: postgres:13  
  odoo:
    image: odoo:latest
    environment:
      HOST: postgres
      USER: username      
      PASSWORD: password

In this case your host name should be 'postgres' instead of '172.17.0.3'. Alternatively you could use 'docker ps' in your console and find out the name (i.e., last column) there. I hope this helps.