What's the difference between Docker Compose vs. Dockerfile [closed]

Answer 1

Dockerfile

A Dockerfile is a simple text file that contains the commands a user could call to assemble an image.

Example, Dockerfile

FROM ubuntu:latest
MAINTAINER john doe 

RUN apt-get update
RUN apt-get install -y python python-pip wget
RUN pip install Flask

ADD hello.py /home/hello.py

WORKDIR /home

---

Docker Compose

Docker Compose

• is a tool for defining and running multi-container Docker applications.

• define the services that make up your app in docker-compose.yml so they can be run together in an isolated environment.

• get an app running in one command by just running docker-compose up

Example, docker-compose.yml

version: "3"
services:
  web:
    build: .
    ports:
    - '5000:5000'
    volumes:
    - .:/code
    - logvolume01:/var/log
    links:
    - redis
  redis:
    image: redis
    volumes:
      logvolume01: {}

Answer 2

Dockerfile and Docker Compose are two different concepts in Dockerland. When we talk about Docker, the first things that come to mind are orchestration, OS level virtualization, images, containers, etc.. I will try to explain each as follows:

Image: An image is an immutable, shareable file that is stored in a Docker-trusted registry. A Docker image is built up from a series of read-only layers. Each layer represents an instruction that is being given in the image’s Dockerfile. An image holds all the required binaries to run.

Container: An instance of an image is called a container. A container is just an executable image binary that is to be run by the host OS. A running image is a container.

Dockerfile: A Dockerfile is a text document that contains all of the commands / build instructions, a user could call on the command line to assemble an image. This will be saved as a Dockerfile. (Note the lowercase 'f'.)

Docker-Compose: Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a YAML file to configure your application’s services (containers). Then, with a single command, you create and start all the services from your configuration. The Compose file would be saved as docker-compose.yml.

Answer 3

Imagine you are the manager of a software company and you just bought a brand new server. Just the hardware.

Think of Dockerfile as a set of instructions you would tell your system adminstrator what to install on this brand new server. For example:

• We need a Debian linux
• add an apache web server
• we need postgresql as well
• install midnight commander
• when all done, copy all *.php, *.jpg, etc. files of our project into the webroot of the webserver (/var/www)

By contrast, think of docker-compose.yml as a set of instructions you would tell your system administrator how the server can interact with the rest of the world. For example,

• it has access to a shared folder from another computer,
• it's port 80 is the same as the port 8000 of the host computer,
• and so on.

(This is not a precise explanation but good enough to start with.)

Answer 4

The Compose file describes the container in its running state, leaving the details on how to build the container to Dockerfiles. http://deninet.com/blog/1587/docker-scratch-part-4-compose-and-volumes

When you define your app with Compose in development, you can use this definition to run your application in different environments such as CI, staging, and production. https://docs.docker.com/compose/production/

It is also seems that Compose is considered production safe as of 1.11, since https://docs.docker.com/v1.11/compose/production/ no longer has a warning not to use it in production like https://docs.docker.com/v1.10/compose/production/ does.

Answer 5

"better" is relative. It all depends on what your needs are. Docker compose is for orchestrating multiple containers. If these images already exist in the docker registry, then it's better to list them in the compose file. If these images or some other images have to be built from files on your computer, then you can describe the processes of building those images in a Dockerfile.

I understand that Dockerfiles are used in Docker Compose, but I am not sure if it is good practice to put everything in one large Dockerfile with multiple FROM commands for the different images?

Using multiple FROM in a single dockerfile is not a very good idea because there is a proposal to remove the feature. 13026

If for instance, you want to dockerize an application which uses a database and have the application files on your computer, you can use a compose file together with a dockerfile as follows

docker-compose.yml

mysql:
  image: mysql:5.7
  volumes:
    - ./db-data:/var/lib/mysql
  environment:
    - "MYSQL_ROOT_PASSWORD=secret"
    - "MYSQL_DATABASE=homestead"
    - "MYSQL_USER=homestead"
  ports:
    - "3307:3306"
app:
  build:
    context: ./path/to/Dockerfile
    dockerfile: Dockerfile
  volumes:
    - ./:/app
  working_dir: /app
      

Dockerfile

FROM php:7.1-fpm 
RUN apt-get update && apt-get install -y libmcrypt-dev \
  mysql-client libmagickwand-dev --no-install-recommends \
  && pecl install imagick \
  && docker-php-ext-enable imagick \
  && docker-php-ext-install pdo_mysql \
  && curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer