The command specified by docker-compose takes precedence over Dockerfile

priority

With docker-compose By specifying dockerfile in build, you can create an image from Dockerfile and create a container.

At this time, there is a CMD that is executed by default in this Dockerfile.

Dockerfile

CMD ["uvicorn", "code.main:app", "--reload", "--host", "0.0.0.0", "--port", "8000"]

With this Dockerfile, try writing another command to command in docker-compose.yml.

docker-compose.yml

version: "3.0"

services:
  fastapi:
    image: "image"
    container_name: "container"
    #Build
    build:
      dockerfile: ./docker/fastapi/Dockerfile
      context: .
    restart: always
    tty: true
    ports:
      - "8000:8000"
    volumes:
      - .:/app
    command: /bin/bash -c "sleep 10 && uvicorn code.main:app --reload --reload-dir code --host 0.0.0.0 --port 8000"

At this time, the command of docker-compose.yml is executed with priority. Therefore, it sleeps for 10 seconds before running uvicorn.

Considering that Dockerfile already exists and you can easily change the behavior with yml, I thought it was a natural behavior.