How to rebuild docker image on push before CI script jobs - docker

Question

I want to generate Dockerfile in GitLab CI script and build it. Then use this newly generated image in build jobs. How can I do this? Tried to use global before_script, but it already starts in default container. I need to do this out of any containers.

Answer 1

before_script is run before every job so it's not something you want. But you can have a first job to do the image build and take advantage of the fact that each job can use a different Docker image. The build of the image is covered in the manual.
Option A (uhm... sort of OK)
Have 2 runners, one with a shell executor (tagged shell) and one with a Docker executor (tagged docker). You would then have a first stage with a job dedicated to building the docker image. It would use the shell runner.
image_build:
stage: image_build
script:
- # create dockerfile
- # run docker build
- # push image to a registry
tags:
- shell
The second job would then run using the runner with docker executor and use this created image:
job_1:
stage: test
image: [image you created]
script:
- # your tasks
tags:
- docker
The problem with this is that the runner would need to be part of the docker group which has security implications.
Option B (better)
The second option would do the same but would have only one runner using Docker executor. The Docker image would be built within a running container (gitlab/dind:latest image) = "docker in docker" solution.
stages:
- image_build
- test
image_build:
stage: image_build
image: gitlab/dind:latest
script:
- # create dockerfile
- # run docker build
- # push image to a registry
job_1:
stage: test
image: [image you created]
script:
- # your tasks