I'm running CI jobs on a self-hosted GitLab instance plus 10 GitLab Runners.
For this minimal example, two Runners are needed:

1. Admin-01
   A shell runner with Docker installed. It can execute e.g. docker build ... to create new images, which are then pushed to the private Docker registry (also self-hosted / part of the GitLab installation)
2. Docker-01
   A docker runner, which executes the previously build image.

On a normal bare-metal, virtual machine or shell runner, I would modify e.g. ~/.profile to execute commands before before_script or script sections are executed. In my use case I need to set new environment variables and source some configuration files provided by the tools I want to run in an image. Yes, environment variables could be set differently, but there seams to be no way to source Bash scripts automatically before before_script or script sections are executed.

When sourcing the Bash source file manually, it works. I also notice, that I have to source it again in script block. So I assume the Bash session is ended between before_script block to script block. Of cause, it's no nice solution to manually source the tools Bash configuration script in every .gitlab-ci.yml file manually by the image users.

myjobn:
  # ...
  before_script:
    - source /root/profile.additions
    - echo "PATH=${PATH}"
    # ...
  script:
    - source /root/profile.additions
    - echo "PATH=${PATH}"
    # ...

The mentioned modifications for e.g. shell runners does not work in images executed by GitLab Runner. It feels like the Bash in the container is not started as login shell.

The minimal example image is build as follows:

1. fetch debian:bullseye-slim from Docker Hub
2. use RUN commands in Dockerfile to modify with some echo outputs
   • /etc/profile
   • /root/.bashrc
   • /root/.profile

# ...

RUN echo "echo GREETINGS FROM /ROOT/PROFILE" >> /root/.profile \
 && echo "echo GREETINGS FROM /ETC/PROFILE" >> /etc/profile \
 && echo "echo GREETINGS FROM /ROOT/BASH_RC" >> /root/.bashrc

When the job starts, non of the echos is printing messages, while a cat shows, the echo commands have been put at the right places while building the image.

At next I tried to modify

• SHELL ["/bin/bash", "-l", "-c"]
  But I assume, this has only effects in RUN commands in the Dockerfile, but not on an executed container.
• CMD ["/bin/bash", "-l"]
  I see no behavior changes.

Question:

1. How to start the Bash in the Docker image managed by GitLab Runner as login shell so it ready configuration scripts?
2. How to modify the environment in a container before before_script or script runs. Modifying means environment variables and execution / sourcing a configuration script or patched default script like ~/.profile.
3. How does GitLab Runner execute a job with Docker?
   This is not documented by GitLab in the official documentation ...
   What I know so far, it jumps between Docker images specified by GitLab and user defined images and shares some directories/volumes or so.

Note:
Yes, the behavior can be achieved with some Docker arguments in docker run, but as I wrote GitLab Runner is managing the container. Alternatively, how to configure, how GitLab Runner launches the images? To my knowledge, there is no configuration option available / documented for this situation.

CodePudding user response：

A shell runner with Docker installed. It can execute e.g. docker build ...

Use docker-in-docker or use kaniko. https://docs.gitlab.com/ee/ci/docker/using_docker_build.html

Shell executor is like "the last resort", where you want specifically to make changes to the server, or you are deploying your application "into" this server.

How to start the Bash in the Docker image managed by GitLab Runner as login shell so it ready configuration scripts?

Add ENTRYPOING bash -l to your image. Or set the entrypoint from gitlab-ci.yml. See docker documentation on ENTRYPOINT and gitlab-ci.yml documentation on image: entrypoint: .

How to modify the environment in a container before before_script or script runs.

Build the image with modified environment. Consult Dockerfile documentation on ENV statements.

Or set the environment from gitlab-ci.yml file. Read documentation on variables: in gitlab-ci.

How to prepare the shell environment in an image executed by GitLab Runner?

Don't. The idea is that the environment is reproducible, ergo, there should be no changes beforehand. Add variables: in gitlab-ci file and use base images if possible.

How does GitLab Runner execute a job with Docker?

This is not documented by GitLab in the official documentation ...

Gitlab is open-source.

What I know so far, it jumps between Docker images specified by GitLab and user defined images and shares some directories/volumes or so.

Yes, first a gitlab-runner-helper is executed - it has git and git-lfs and basically clones the repository and downloads and uploads the artifacts. Then the container specified with image: is run, cloned repository is copied into it and a specially prepared shell script is executed in it.