Using GitLab CI/CD to build and store container images

Often building container images consume a lot of bandwidth and back at home I don’t have a good internet connection to build images again and again.

Also, there are times when I have to, again and again, push the container images to Docker hub in a short period. I felt that they tend to slow down the upload speeds when I do this. (I’m not sure how accurate is this observation.)

Instead of Docker Hub to host the repository and building images on my local machine, I thought of using GitLab’s CI/CD to do the job.

Setting up repository to build and store container images

Create a new Project in GitLab.
Create a new file Docker.gitlab-ci.yml in the master branch as a template to use when we will use CI/CD pipeline to build the docker images.

#Docker.gitlab-ci.yml

build:image:
  image: docker:stable
  services:
    - docker:dind

  variables:
    DOCKER_HOST: tcp://docker:2375
    DOCKER_DRIVER: overlay2
    IMAGE_NAME: hello                           # CHANGE IMAGE NAME
    TAG: latest                                 # EDIT TAG

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

  script:
    - docker build --pull -t $CI_REGISTRY_IMAGE/$IMAGE_NAME:$TAG .
    - docker push $CI_REGISTRY_IMAGE/$IMAGE_NAME:$TAG

Building a container Image

Create a new branch from master.
```
 git checkout -b flask-app
```
Add required files and Dockerfile to the branch.
Use the Docker.gitlab-ci.yml template to create a new .gitlab-ci.yml file which will build the image.
Remember: Change the variable IMAGE_NAME in the yaml file with the name of the image.
Push the changes and naviage to CI/CD and Container Registry section of the project to see the image build and stored images.

I use this GitLab repository to do the job. You can clone it and get started without doing the above steps.