How to enable GitLab Container Registry and push docker image in it

What are the exact steps to enable Container Registry in GitLab Community Edition 14.2.4 using the domain method, and how can I push a docker image to the registry? Also, how can I integrate GitLab CI with the registry?

Specifying only the following string as described in "Configure Container Registry under its domain" not working for GitLab Community Edition 14.2.4

registry_external_url 'registry.gitlab.example.com'

This is a self-answering topic, I will guide you through the steps to enable Container Registry in GitLab Community Edition 14.2.4 and how to push a Docker image.

Step 1: To enable Container Registry, I used the domain method(configuration under existing domain described here). Edit your /etc/gitlab/gitlab.rb file and add the following lines of code:

registry_external_url 'https://registry.example.com'

gitlab_rails['registry_enabled'] = true
gitlab_rails['registry_host'] = "registry.example.com"

registry['enable'] = true
registry['registry_http_addr'] = "localhost:5000"
registry['log_directory'] = "/var/log/gitlab/registry"
registry['env_directory'] = "/opt/gitlab/etc/registry/env"
registry_nginx['enable'] = true
registry_nginx['listen_port'] = 443
registry_nginx['ssl_certificate'] = "/etc/gitlab/ssl/registry.example.com/fullchain.pem"
registry_nginx['ssl_certificate_key'] = "/etc/gitlab/ssl/registry.example.com/privkey.pem"

After adding these lines, run gitlab-ctl reconfigure. Note that I tried different approaches, including specifying only the registry_external_url URL, but nothing worked until I used the above setup. In this article I skipped the security certification steps, this step could be done differently. I have used Let's Encrypt certificates pre-generated and specified for the registry. More information here

Step 2: Once Container Registry is enabled, you can find it in GitLab by navigating to Project -> Packages & Registries -> Container Registry. On the empty page, you will find help commands to start working with the registry.

Step 3: To integrate GitLab CI with Container Registry, add the following code to your .gitlab-ci.yml file:

create-image:
  stage: build
  tags:
    - shell
  variables:
    VER: 1.0-${CI_PIPELINE_ID}
    ID: ${CI_COMMIT_SHORT_SHA}
    GIT_SUBMODULE_STRATEGY: recursive
  before_script:
    - echo "Docker registry url is $CI_REGISTRY"
    - echo "Docker registry username is $CI_REGISTRY_USER"
    - echo "Docker registry repo is $CI_REGISTRY_IMAGE"
  timeout: 12h
  script:
    - docker build -t ${CI_REGISTRY_IMAGE}:$VER ${CI_PROJECT_DIR}

upload-to-registry:
    stage: deploy
    when: manual
    tags:
       - shell
    script:
        - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
        - docker push ${CI_REGISTRY_IMAGE}:$VER