Use of `build` directive to build sample postgres database

docker-compose-filladb.sh

# Make a directory `db` encapsulates your image, having 
# a docker-compose at the same level.
$ tree
.
├── db
│   ├── Dockerfile
│   └── init
│       └── 01-filladb.sh
└── docker-compose.yml

2 directories, 3 files


# in the docker-compose file, reference the image directory
# in the `build` property. This makes `docker-compose` build
# the directory as an image and then use it when creating 
# containers. 
$ cat docker-compose.yml 
version: '3.2'
services:
  postgres:
    restart: 'always'
    ports:
      - '5432:5432'
    environment:
      - "FILLA_DB_USER=filla"
      - "FILLA_DB_PASSWORD=filla"
      - "FILLA_DB_DATABASE=filladb1"
      - "POSTGRES_PASSWORD=password"
    build: './db'
    networks:
      infranet:
        aliases:
          - 'postgres'

networks:
  infranet: