Docker image with PHP, Composer and Docker installed - docker

Question

I use Gitlab.com for my CI using their shared docker runners. I have a project which requires PHP and composer installed, while it also needs docker to build a docker image of the project.
I've tried for hours to build a docker image which has PHP, composer and docker installed, but I can't seem to figure it out.
For reference, my gitlab-ci.yml file looks like this;
image: docker:latest
variables:
DOCKER_DRIVER: overlay2
services:
- docker:dind
composer:install:
stage: build
artifacts:
paths:
- /
expire_in: 1 week
script:
- docker run --rm --interactive --tty --volume $PWD:/app composer install
build:image:
stage: build
dependencies:
- composer:install
script:
- docker login registry.gitlab.com -u $REGISTRY_USERNAME -p $REGISTRY_PASSWORD
- docker build -t registry.gitlab.com/accountname/projectname/develop .
- docker push registry.gitlab.com/accountname/projectname/develop
Using the sample build script provided by Stefan below, I put together the following build file which appears to work perfectly. It builds the project using the project Dockerfile, and pushed the resulting image to my Gitlab repository.
image: docker:latest
variables:
DOCKER_DRIVER: overlay2
services:
- docker:dind
before_script:
- docker run --rm --volume $PWD:/app composer install
build:image:
stage: build
script:
- docker login registry.gitlab.com -u $REGISTRY_USERNAME -p $REGISTRY_PASSWORD
- docker build -t registry.gitlab.com/accountname/projectname/develop .
- docker push registry.gitlab.com/accountname/projectname/develop

Answer 1

You should use a 2 job CI and use the artifact feature provided by Gitlab to pass the composer install result as dependencies between jobs.
Your first job (composer:install) could use something like https://hub.docker.com/r/library/composer/ in your script section to install all composer packages, then pass it to the build:image job that builds your Docker image.
This would roughly look like this:
image: docker:latest
variables:
DOCKER_DRIVER: overlay2
services:
- docker:dind
composer:install:
stage: composer
artifacts:
paths:
- /
expire_in: 1 week
script:
- docker run --rm --interactive --tty --volume $PWD:/app composer install
build:image:
stage: build
dependencies:
- composer:install
script:
- docker build -t myimage:latest .
Where your Dockerfile could be something like this (based on this):
FROM php:7.0-cli
COPY . /usr/src/myapp
WORKDIR /usr/src/myapp
CMD [ "php", "./your-script.php" ]