gitlab-ci pipline for building docker containers, tagging the code in git and pushing the new generated container into your docker registry.

.gitlab-ci.yml

image: docker:latest
services:
    - docker:dind
stages:
    - Dev
    - Dev-publish
    - Prod-Tag
    - Prod-publish
variables:
    REGISTRY: [Your Registry]
    REPOSITORY: [Your Repository]

before_script:
    # check for VERSION file
    - if [ ! -f VERSION ]; then echo "VERSION file not found!"; exit 1; else export VERSION=$(cat VERSION); fi
    - 'echo "Running Pipeline for: $REGISTRY/$REPOSITORY:${VERSION}"'

build:
    stage: Dev
    script:
        - docker build -t $REGISTRY/$REPOSITORY .
        - docker save $REGISTRY/$REPOSITORY > image.tar
        - docker image ls
    artifacts:
        paths:
            - image.tar
    only:
        - master

dev-publish:
    stage: Dev-publish
    dependencies: 
        - build
    script:
        # check for $REGISTRY_USER and $REGISTRY_PW file
        - if [ -z ${REGISTRY_USER+x} ]; then echo "REGISTRY_USER is not set!"; exit 1; fi
        - if [ -z ${REGISTRY_PW+x} ]; then echo "REGISTRY_PW is not set!"; exit 1; fi
        # login into docker registry
        - docker login -u $REGISTRY_USER -p $REGISTRY_PW $REGISTRY
        # load previously generated docker image
        - docker load -i image.tar
        # push to docker registry
        - docker tag $REGISTRY/$REPOSITORY:latest $REGISTRY/$REPOSITORY:latest-dev
        - docker push $REGISTRY/$REPOSITORY:latest-dev
    only:
        - master

publish:
    stage: Prod-publish
    dependencies:
        - build
        - tag
    script:
        # check for $REGISTRY_USER and $REGISTRY_PW file
        - if [ -z ${REGISTRY_USER+x} ]; then echo "REGISTRY_USER is not set!"; exit 1; fi
        - if [ -z ${REGISTRY_PW+x} ]; then echo "REGISTRY_PW is not set!"; exit 1; fi
        # login into docker registry
        - docker login -u $REGISTRY_USER -p $REGISTRY_PW $REGISTRY
        # load previously generated docker image
        - docker load -i image.tar
        # push to docker registry
        - docker tag $REGISTRY/$REPOSITORY:latest $REGISTRY/$REPOSITORY:$VERSION
        - docker push $REGISTRY/$REPOSITORY:$VERSION
    only:
        - master

tag:
    image: python:3.7-stretch
    stage: Prod-Tag
    script:
        - mkdir -p ~/.ssh && chmod 700 ~/.ssh
        - ssh-keyscan gitlab.com >> ~/.ssh/known_hosts && chmod 644 ~/.ssh/known_hosts
        - eval $(ssh-agent -s)
        - echo -n "$SSH_DEPLOY_KEY" | tr -d '\r' | ssh-add - > /dev/null
        - chmod +x tag.py
        - ./tag.py
    when: manual
    allow_failure: false
    only:
        - master

readme.md

Gitlab CI for docker build, git tag and push to docker registry

Setup

1. Copy .gitlab-ci.yml, tag.py and readme.md into your repository
2. Update .gitlab-ci.yml with your registry and repository. Therefore, change:

REGISTRY: [Your Registry]
REPOSITORY: [Your Repository]

to e.g.

REGISTRY: registry.hub.docker.com/library
REPOSITORY: iwanbolzern/finals

3. Create gitlab secret for REGISTRY_USER, REGISTRY_PW. It's the username and password of your docker registry! In your Project go to Settings > CI/CD > Variables and create the two variables.
4. Create Deploy Key with write access to your repository and add it as SSH_DEPLOY_KEY to variables. First you have to create a public and private key. To do so, open your git-bash and type: ssh-keygen -o -t rsa -b 4096 -C "email@example.com" -f ssh-key. Copy the public key to token in Settings > Repository > Deploy Keys and the private key into your variables.

tag.py

#!/usr/bin/env python3
import os
import re
import sys
import subprocess


def git(*args):
    return subprocess.check_output(['git'] + list(args))


def tag_repo(tag):
    url = os.environ['CI_REPOSITORY_URL']

    # Transforms the repository URL to the SSH URL
    # Example input: https://gitlab-ci-token:xxxxxxxxxxxxxxxxxxxx@gitlab.com/threedotslabs/ci-examples.git
    # Example output: git@gitlab.com:threedotslabs/ci-examples.git
    push_url = re.sub(r'.+@([^/]+)/', r'git@\1:', url)

    git('remote', 'set-url', '--push', 'origin', push_url)
    git('tag', tag)
    git('push', 'origin', tag)


def main():
    if 'VERSION' not in os.environ:
        print('VERSION not set')
        return -1
    version = os.environ['VERSION']

    # check if version already exists
    tags = git('describe', '--tags', '--always').decode().strip()
    if version in tags:
        print('Version already exists!')
        return -1

    tag_repo(version)

    return 0


if __name__ == '__main__':
    sys.exit(main())

VERSION

1.0.0