Can a Dockerfile extend another one?

Question

I have a Dockerfile for PHP like this :

FROM php:7-fpm
ENV DEBIAN_FRONTEND noninteractive

RUN apt-get update && \
    apt-get install -y git libicu-dev libmagickwand-dev libmcrypt-dev libcurl3-dev jpegoptim
RUN pecl install imagick && \
    docker-php-ext-enable imagick

RUN docker-php-ext-install intl
RUN docker-php-ext-install pdo_mysql
RUN docker-php-ext-install opcache
RUN docker-php-ext-install mcrypt
RUN docker-php-ext-install curl
RUN docker-php-ext-install zip

And I'd like to create another Dockerfile, based on the first one, but with some PHP extensions added (for dev purpose) : Xdebug and other stuffs.

Can I create a "dev" Dockerfile that extends my main Dockerfile (without rewrite it) ?

Answer 1

Using multi-stage build is definitely one part of the answer here.

docker-compose v3.4 target being the second and last.

Here is a example to have 2 containers (1 normal & 1 w/ xdebug installed) living together :

Dockerfile

FROM php:7-fpm AS php_base 
ENV DEBIAN_FRONTEND noninteractive

RUN apt-get update && \
    apt-get install -y git libicu-dev libmagickwand-dev libmcrypt-dev libcurl3-dev jpegoptim
RUN pecl install imagick && \
    docker-php-ext-enable imagick

RUN docker-php-ext-install intl
RUN docker-php-ext-install pdo_mysql
RUN docker-php-ext-install opcache
RUN docker-php-ext-install mcrypt
RUN docker-php-ext-install curl
RUN docker-php-ext-install zip

FROM php_base AS php_test

RUN pecl install xdebug 
RUN docker-php-ext-enable xdebug

docker-compose.yml

version: '3.4'

services:
  php:
    build:
      context: ./
      target: php_base

  php_test:
    build:
      context: ./
      target: php_test
  
# ...

Answer 2

If you don't want to tag your first Dockerfile in order to use it in a FROM instruction in your next Dockerfile, and you are using Docker 20.10+, you can also do this:

# syntax = edrevo/dockerfile-plus

INCLUDE+ Dockerfile.base

RUN whatever

The INCLUDE+ instruction gets imported by the first line in the Dockerfile. You can read more about the dockerfile-plus at https://github.com/edrevo/dockerfile-plus

Answer 3

That is exactly what your FROM php:7-fpm is doing: extending the Dockerfile from the php image (with 7-fpm tag) with the contents of your Dockerfile.

So after building an image from your Dockerfile:

docker build -t my-php-base-image .

You can extend that by creating a new Dockerfile that starts with:

FROM my-php-base-image

Answer 4

Sand is a small open source tool I wrote to address this need (and many others) by allowing you to write your dockerfiles in a python-like syntax that enables you to share code between them.

Given the following directory structure:

my-monorepo/
│
├── tweet-service/
|   ├── src/
|   ├── ...
│   └── Sandfile
│
├── home-timeline/
|   ├── src/
|   ├── ...
│   └── Sandfile
│
└── Sandfile

You can write your Sandfiles like this:

# ./my-monorepo/Sandfile
from sand import *

def MyService(name):
    From("ubuntu", "20.04")
    Run("apt-get install python3")
    Copy(Src="src", Dst="/app")
    Entrypoint(f"python3 /app/{name}.py")

Sand("tweet-service")
Sand("home-timeline")

# ./my-monorepo/tweet-service/Sandfile
from sand import *

MyService("tweet-service") # Defined in ../Sandfile

# ./my-monorepo/home-timeline/Sandfile
from sand import *

MyService("home-timeline") # Defined in ../Sandfile

This allows you to share code between your Dockerfiles, and keep them DRY.

This is similar to the way add_subdirectory works in CMake

Answer 5

Hello folk's to the needs of factorization on Dockerfile I developed this buildkit custom syntax frontend plugin: devthefuture/dockerfile-x

just one line at the top of file # syntax = devthefuture/dockerfile-x and that's it !

# syntax = devthefuture/dockerfile-x

FROM ./base/dockerfile

COPY --from=./build/dockerfile#build-stage /app /app

INCLUDE ./other/dockerfile

this was inspired by @edrevo works