Build and push a Docker image to a private registry with Gitlab CI

Being able to create and host private Docker images for use in your team is a great way of speeding up development processes without having to publicly share your code. For example. at Liquid Light we have a Docker image with a private NPM token embedded for deployment of our packages.

In this post we'll build and push our Docker image to a private registry using Gitlab CI.

Create your Dockerfile

First thing you'll need is a Dockerfile, I won't go into too much depth here as each Docker image will have a different purpose. As an example, we could have a Docker image that is a copy of the latest Debain image bit with Git installed

FROM debian:latest

RUN apt install git

Create a Dockerfile in a new repository and set your commands

Build locally

Before pushing to Gitlab, make sure you can build your image locally

docker build .

This might give it a random generated name, but will at least tell you if your Dockerfile is correct

Create a Gitlab file

Next to your Dockerfile, create a .gitlab-ci.yml file - this is going to run on Gitlab to build your Docker image

image: docker:19.03

stages:
  - build

variables:
  DOCKER_TLS_CERTDIR: "/certs"

services:
  - docker:19.03.13-dind

before_script:
  - echo "$DOCKER_REGISTRY_PASS" | docker login $DOCKER_REGISTRY --username $DOCKER_REGISTRY_USER --password-stdin

build:
  stage: build
  script:
    - >
      docker build
      --no-cache
      --tag $DOCKER_IMAGE_NAME:latest
      .
    - docker push $DOCKER_IMAGE_NAME:latest

This yaml does the following:

• Uses a docker image and enables the dind (Docker in Docker) service - this allows Docker to build Docker
• Before the script starts, it logs into your Docker registry
• Lastly, in the build stage, it builds your Docker image and pushes it to the registry.

There are a few variables you need set up in your CI/CD config

• $DOCKER_REGISTRY - the URL to your Docker registry
• $DOCKER_REGISTRY_USER - The username to login to your private Docker registry
• $DOCKER_REGISTRY_PASS - The password to login to your private Docker registry
• $DOCKER_IMAGE_NAME - The full name of your Docker image (if you have enabled and are using the Gitlab container registry, you can replace this with $CI_REGISTRY_IMAGE which contains the full image name/path you want)