Extend docker postgres image to create extra database

I've already seen this topic : https://stackoverflow.com/a/26599273/2323245

But I have the following problem :

postgres_1  | FATAL:  role "docker" does not exist
app_1       | Error: Could not establish a connection with the database

This is my docker-compose.yml file

version: "2"

services:
  app:
    build:
      context: .
      dockerfile: Dockerfiles/app.dockerfile
    links:
      - postgres
    depends_on:
      - postgres
    ports:
      - "8080:8080"
    environment:
      PORT: 8080
    networks:
      - neo_dev
    restart: always

  postgres:
    build:
          context: .
          dockerfile: Dockerfiles/postgres.dockerfile
    networks:
      - neo_dev
    volumes:
      - postgresql:/var/lib/postgresql
      # This needs explicit mapping due to https://github.com/docker-library/postgres/blob/4e48e3228a30763913ece952c611e5e9b95c8759/Dockerfile.template#L52
      - postgresql_data:/var/lib/postgresql/data
    ports:
      - "5430:5432"  #in case you already have postgres running in your host machine

networks:
    neo_dev:
      driver: bridge

volumes:
  postgresql:
  postgresql_data:

My postgres.dockerfile is

FROM library/postgres

MAINTAINER Samir Bouaked "sbouaked@neocasesoftware.com"

ADD Dockerfiles/init.sql /docker-entrypoint-initdb.d/

And this is my init.sql file

CREATE USER docker with password 'docker';
CREATE DATABASE docker;
GRANT ALL PRIVILEGES ON DATABASE docker TO docker;

In my golang app, i'm trying to reach the database with

router.GET("/db", func(c *gin.Context) {
		db, err := sql.Open("postgres", "host=postgres port=5432 user=docker dbname=docker password=docker sslmode=disable")
		if err != nil {
			log.Fatal("Error: The data source arguments are not valid - " + err.Error())
		}
		err = db.Ping()
		
		if err != nil {
			log.Println("Error: Could not establish a connection with the database")
			c.String(http.StatusOK, "hotstName : %s\nDbStatus : %s", os.Getenv("HOSTNAME"), err)
		} else {
			c.String(http.StatusOK, "\nhotstName : %s\nDbStatus : connection ok !\n", os.Getenv("HOSTNAME"))
		}
		defer db.Close()
	})

I tried different solutions like passing directly in the dockerfile env variables like that

ENV POSTGRES_USER docker
ENV POSTGRES_PASSWORD docker
ENV POSTGRES_DB docker

But have always the same result...
For more information you can check this repo https://github.com/neocase/docker-go-starter-kit

I don't understand the problem

It was a problem of docker volume.

I have to docker volume rm postgresvolume and do again a docker-compose up --build

It wasn't a problem of environment variables, but juste the fact that the init.sql was in cash and not run at the begining. It's due to some test I make a the start of the project

If you want to create the DB by passing ENV variables using docker-compose you can specify something like

  postgres:
    container_name: postgres
    image: library/postgres
    ports:
      - "5432:5432"
    environment:
      - POSTGRES_DATABASE=docker
      - POSTGRES_USER=docker
      - POSTGRES_PASSWORD=docker
      - POSTGRES_ADMIN_PASSWORD=docker

in your compose YML file.
This should create you a postgres container with an DB docker with user/pwd docker, no need for your own dockerfile anymore (so you can use any postgres image that supports this behavior)

After running compose (and if it doesn't work as you expect) you should have a look at the logs if your postgres container is working at all, or if there is an issue with your app.