Seeking help understanding workflow for C++ Docker CI project

GitLab CI/CD
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1

Hello,

I’m looking to understand how to properly structure my .gitlab-ci.yml and Dockerfile such that I can build a C++ application into a Docker container.

I’m struggling with where the actual compilation and link of the C++ application should take place within the CI workflow.

What i’ve done:

  • My current in approach is to use Docker in Docker with a private gitlab docker registry.
  • My gitlab-ci.yml uses a dind docker image service I created based on the the docker:19.03.1-dind image but includes my certificates to talk securely to my private gitlab docker registry.
  • I also have a custom base image referenced by my gitlab-ci.yml based on docker:19.03.1 that includes what I need for building, eg cmake, build-base mariadb-dev, etc.
  • Have my build script added to the gitlab-ci.yml to build the application, cmake … && cmake --build .
  • The dockerfile then copies the final binary produced in my build step.

Having done all of this it doesn’t feel quite right to me and I’m wondering if I’m missing the intent. I’ve tried to find a C++ example online to follow as example but have been unsuccessful.

What I’m not fully understanding is the role of each player in the docker-in-docker setup: docker image, dind image, and finally the container I’m producing…

What I’d like to know…

  • Who should perform the build and contain the build environment, the base image specified in my .gitlab-ci.yml or my Dockerfile?
  • If I build with the dockerfile, how to i get the contents of the source into the docker container? Do I copy the /builds dir? Should I mount it?
  • Where to divide who performs work, gitlab-ci.yml or Docker file?
  • Reference to a working example of a C++ docker application built with Docker-in-Docker Gitlab CI.

.gitlab-ci.yml

image: $CI_REGISTRY/building-blocks/dev-mysql-cpp:latest
#image: docker:19.03.1

services:
  - name: $CI_REGISTRY/building-blocks/my-dind:latest
    alias: docker

stages:
  - build
  - release

variables:
  # Use TLS https://docs.gitlab.com/ee/ci/docker/using_docker_build.html#tls-enabled
  DOCKER_TLS_CERTDIR: "/certs"
  CONTAINER_TEST_IMAGE: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG
  CONTAINER_RELEASE_IMAGE: $CI_REGISTRY_IMAGE:latest

before_script:
        - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY

build:
  stage: build
  script:
    - mkdir build
    - cd build
    - cmake ..
    - make -j4
    - cd ..
    - docker build --pull -t $CONTAINER_TEST_IMAGE .
    - docker push $CONTAINER_TEST_IMAGE

release-image:
  stage: release
  script:
    - docker pull $CONTAINER_TEST_IMAGE
    - docker tag $CONTAINER_TEST_IMAGE $CONTAINER_RELEASE_IMAGE
    - docker push $CONTAINER_RELEASE_IMAGE
  only:
    - master

Thanks,
Matt