### Dockerfile

FROM crystallang/crystal

WORKDIR /usr/app

COPY ./ ./

RUN shards install



### docker-compose.yml

version: "3"

services:
  blog:
    build: .
    command:
      - /bin/sh
      - -c
      - |
        sh checkshards.sh
        crystal run ./src/main.cr
    volumes:
      - .:/usr/app
      - ./.shards:/usr/app/.shards
    ports:
      - "3000:3000"
    depends_on:
      - postgres
    environment:
      PG_USER: usr
      PG_PW: pw
      PG_DB: usr

  postgres:
    image: postgres:10.3-alpine
    volumes:
      - ./data:/custom/path/to/data
    ports:
      - "5432:5432"
    environment:
      POSTGRES_PASSWORD: pw
      POSTGRES_USER: usr
      PGDATA: /custom/path/to/data



### checkshards.sh

if shards check | grep 'shards install'
then
		shards install
else
		echo 'All the shards are installed. Will continue building docker.'
fi