docker-compose-wait-for-it

docker-compose.yml

version: "3.8"

services:
  terminal:
    image: sh
    link:
      - db
    # this will wait for db and then execute the next command after each `-s --`
    entrypoint: wait-for-it.sh db:5432 -s -- /usr/local/bin/shush exec -- -s -- echo "night moon"
    command: sh
    environment:
      # magic link referring to database service name done by compose
      DB_HOST: db
      DB_PASSWORD: "must_set"

  db:
    image: postgres:12-alpine
    restart: always
    ports:
      - "5435:5432"
    volumes:
      # to preserve database data from docker
      - ./tmp/db-data:/var/lib/postgresql/data
    environment:
      POSTGRES_PASSWORD: "must_set"

Dockerfile

From whatever

# Install wait-for-it.sh docker-compose to wait on dependent containers e.g. database
RUN apk --no-cache --virtual .build-deps add curl && \
    curl https://raw.githubusercontent.com/raphaelahrens/wait-for-it/master/wait-for-it.sh > /usr/local/bin/wait-for-it.sh && \
    chmod +x /usr/local/bin/wait-for-it.sh && \
    apk del .build-deps

ENTRYPOINT ["/usr/local/bin/shush", "exec", "--"]