Dockerized PostgreSQL: FATAL: password authentication failed for user "postgres

I have a dockerized PSQL instance and a dockerized app that connects to it. I am getting an incorrect password error trying to connect despite never setting one. Default of postgres doesn’t work.

compose.yml

services:
  psql:
    build: database/.
    env_file: vars.env
    ports:
      - "5432:5432"
  reader:
    build: reader/.
    env_file: vars.env
    restart: always

reader.py

import psycopg2

connection = psycopg2.connect(
    database="postgres",
    user="postgres",
    password="postgres",
    host="psql",
    port=5432)

cursor = connection.cursor()

Error

psycopg2.OperationalError: connection to server at "psql" (172.29.0.3), port 5432 failed: FATAL:  password authentication failed for user "postgres"

What could this password be? Or how is it set. I thought no default user or pass was set.

>Solution :

You have to make sure the vars.env file has these:

POSTGRES_USER=postgres
POSTGRES_PASSWORD=postgres

For trouble shooting I’d remove the vars.env and uses a direct environment variable as the docs suggests, to see if it works:

  psql:
    image: postgres
    restart: always
    environment:
      POSTGRES_PASSWORD: postgres

From docs:

The PostgreSQL image uses several environment variables which are easy
to miss. The only variable required is POSTGRES_PASSWORD, the rest are
optional.