Load Postgres dump after docker-compose up

Reading https://hub.docker.com/_/postgres/, the section 'Extend this image' explains that any .sql in /docker-entrypoint-initdb.d will be executed after build.

I just needed to change my Dockerfile.db to:

FROM postgres

ADD ./devops/db/dummy_dump.sql /docker-entrypoint-initdb.d

And it works!

Another option that doesn't require a Dockerfile would be to mount your sql file into the docker-entrypoint-initdb.d folder using the volumes attribute of docker-compose. The official postgres image https://hub.docker.com/_/postgres/ will import and execute all SQL files placed in that folder. So something like

services:
  postgres:
    environment:
      POSTGRES_DB: my_db_name
      POSTGRES_USER: my_name
      POSTGRES_PASSWORD: my_password
  volumes:
    - ./devops/db/dummy_dump.sql:/docker-entrypoint-initdb.d/dummy_dump.sql

This will automatically populate the specified POSTGRES_DB for you.