从 dockerfile 访问 docker-compose.yml 中设置的卷

Question

I have my project architecture like this:

.
├── app/
├── context/
│   ├── Dockerfile
│   ├── .dockerignore
│   └── php.ini
├── database/
├── http/
├── composer.json
└── docker-compose.yml

and in docker-compose.yml I have the following configuration:

version: '3.8'
services: 
  app:
    container_name: "ERP"
    restart: always
    build: 
      context: ./context
      dockerfile: Dockerfile
    stdin_open: true
    tty: true
    ports: 
      - '8000:80'
    links: 
      - db_server
    volumes:
      - .:/usr/src/app
    working_dir: /usr/src/app
  db_server:
    container_name: "db_server"
    image: 'mysql:8.0'
    ports: 
    - '3306:3306'

But when I set the Dockerfile content to set up the application with docker-compose up , having Dockerfile content as this:

FROM ubuntu:20.04
WORKDIR /usr/src/app
RUN cat composer.json

It says "No such file or directory composer.json" . Why?

UPDATE

I managed to solve the problem based on ENTRYPOINT configuration..

as far I understand - I'm new to docker -, the ENTRYPOINT defines an entry script running at the beginning of a container, thus, starting that script will be definitely in the run time of the container and after the initializations specified by docker-compost.yml file.. so the contents of the actual context will be available to the script to see it in the time it runs..

Thank you all for your answers.

Answer 1

That's because you define the context to be "./context", so you are stuck into this folder, where composer.json isn't.

Use "." for the context. and context/Dockerfile for the dockerfile. Then mounting '.' will mount the whole directory, and not only the./context one.

Answer 2

The build process to create an image occurs before the runtime process that takes that image and runs a container. The compose file includes a build section to allow you to easily build the image before running it, but all of the other parts of the compose file define runtime configurations like volume mounts and networking.

At build time, you do not get to specify the volume sources, at most you can define a required volume target in the image with a VOLUME step. (Note if you do that, future RUN steps within the Dockerfile may have issues modifying that directory since many build tools mount an anonymous volume as you've requested, but only capture the changes to the container filesystem, not the volume filesystem).

If you need the contents of a file or directory in your image, you must perform a COPY or ADD step in the Dockerfile to copy from the build context (typically imported as . or the current directory) into the image.

Answer 3

Key build.context define a path to a directory containing a Dockerfile . This is a context of building image, and during build process docker doesn't have access to composer.json file (it is out of the context).

Command RUN runs command during build. If you want to run it when container is starting, you should use CMD .

FROM ubuntu:20.04
WORKDIR /usr/src/app
CMD cat composer.json