docker-compose使用旧卷

Question

I am trying to set up a CI pipeline with docker-compose and am struggling to understand how named volumes work...

As part of my Dockerfile, I copy in the application files and then run composer install to install the application dependencies. There are some elements of the applicaton files and the dependencies that I want to share with the other containers that are running / are set up to be run to perform utility processes (such as running database migrations). See the example below:

Dockerfile:

FROM php:5.6-apache

# Install dependencies
COPY composer.* /app/
RUN composer install --no-dev

# Copy application files
COPY bin bin
COPY environment.json environment.json

VOLUME /app

docker-compose.yml

 web:
    build:
      context: .
      dockerfile: docker/web/Dockerfile
    volumes:
      - app:/app
      - ~/.cache/composer:/composer/cache

  migrations:
    image: my-image
    depends_on:
      - web
    environment:
      - DB_DRIVER=pdo_mysql
      - AUTOLOADER=../../../vendor/autoload.php
    volumes:
      - app:/app
    working_dir: /app/vendor/me/my-lib

volumes:  
  app:

In the example above (irrelevant information omitted), I have a "migrations" service that pulls the migrations from the application dependencies installed with composer. My idea is that when I perform docker-compose build followed by docker-compose up , it will bring up the latest version of software with the latest dependencies and run the latest migrations at the same time.

This works fine the first time. Unfortunately on subsequent runs I cannot get docker-compose to use the new versions. If I run docker-compose build , I can see the composer install run and install all the latest libraries, but then when I go into the container with docker-compose run web /bin/bash , the old dependencies are in there! If I run the image directly with docker run web_1 , I can see all the latest files no problem. So it's definitely a compose-specific problem.

I assume I need to do something like clear out the volume cache, but whatever I have tried doesn't seem to work. I can only assume I am misunderstanding the idea of volumes.

Any help would be hugely appreciated. Thanks!

Answer 1

The problem here has to do with mounting a volume over a location defined in the build. The first build of the image has composer put its output into /app , and the first run of the first build mounts the app named volume to /app . This clobbers the image version of /app with a new write-layer on top. Mounting this named volume on the second build of the image will keep the original contents of /app .

Instead of using a named volume, use volumes-from to load the exported /app volume from web into the migration container.

version: '2'
services:
  web:
    build:
      context: .
      dockerfile: docker/web/Dockerfile
    volumes:
      - ~/.cache/composer:/composer/cache
  migrations:
    image: docker-registry.efficio.digital:5043/doctrine-migrator:1.1
    depends_on:
      - web
    environment:
      - DB_DRIVER=pdo_mysql
      - AUTOLOADER=../../../vendor/autoload.php
    volumes_from:
      - web:ro 

Answer 2

What I understand from your question is you want to run composer install every time you run your container. In that case you have to use CMD instruction to execute that command.

CMD composer install --no-dev

RUN and CMD are both Dockerfile instructions.

RUN lets you execute commands inside of your Docker image. These commands get executed once at build time and get written into your Docker image as a new layer.

For example if you wanted to install a package or create a directory inside of your Docker image then RUN will be what you'll want to use. For example, RUN mkdir -p /path/to/folder.

CMD lets you define a default command to run when your container starts.

You could say that CMD is a Docker run-time operation, meaning it's not something that gets executed at build time. It happens when you run an image. A running image is called a container.