How to Automate Docker Image Deployment with GitLab’s CI/CD

Once you know how to create an efficient Docker image, automating the deployment process is a natural next step. This article will teach you how to automate the building and deployment of a Docker image to a registry using GitLab’s Continuous Integration and Deployment (CI/CD) pipeline.

Setting Up the GitLab Pipeline

GitLab CI/CD is an excellent tool for automating the build and deployment of Docker images. We’ll use a .gitlab-ci.yml file to define the pipeline configuration. This pipeline will have a single stage called builder for building and pushing the Docker image.

Pipeline Breakdown

Step 1: Variables

variables:
  DOCKER_IMAGE_CI: whitecanvas/builder:$CI_COMMIT_TAG

We define a variable DOCKER_IMAGE_CI that contains the Docker image name along with a tag. $CI_COMMIT_TAG is a predefined variable in GitLab CI/CD that uses the tag name of the commit if present (this pipeline will be executed only when the user creates a tag number).

Step 2: Authentication

before_script:
  - echo "$DOCKERHUB_PASS" | docker login --username $DOCKERHUB_USER --password-stdin

Before executing the main scripts, we log in to Docker Hub using credentials stored in the GitLab CI/CD variables DOCKERHUB_USER and DOCKERHUB_PASS.

Step 3: Building and Pushing the Image

amd64_image:
  only:
    - /(\d+\.)?(\d+\.)?(\*|\d+)/
  stage: builder
  image: docker:latest
  services:
    - docker:dind
  script:
    - cd amd64
    - docker build -t $DOCKER_IMAGE_CI .
    - docker push $DOCKER_IMAGE_CI

This job runs only when the commit is tagged with a version number (e.g., 1.0.0). It uses the docker:latest image and docker:dind (Docker in Docker) service.

The script performs the following steps:

1. Change Directory: Moves into the amd64 directory to where the Dockerfile is located.
2. Build the Image: Executes docker build with the tag specified in DOCKER_IMAGE_CI.
3. Push the Image: Pushes the built image to Docker Hub.

Full Contents of the .gitlab-ci.yml File

Here’s the full contents of the .gitlab-ci.yml file.

stages:
  - builder

variables:
  DOCKER_IMAGE_CI: whitecanvas/builder:$CI_COMMIT_TAG

before_script:
  - echo "$DOCKERHUB_PASS" | docker login --username $DOCKERHUB_USER --password-stdin

amd64_image:
  only:
    - /(\d+\.)?(\d+\.)?(\*|\d+)/
  stage: builder
  image: docker:latest
  services:
    - docker:dind
  script:
    - cd amd64
    - docker build -t $DOCKER_IMAGE_CI .
    - docker push $DOCKER_IMAGE_CI

Automate Your Docker Image Deployments Using GitLab

By leveraging GitLab’s CI/CD pipeline, we can automate the building and deployment of a Docker image.

This setup ensures that every time a new tag is pushed to the repository, our image is automatically built and updated on Docker Hub, streamlining the deployment process and maintaining consistency across releases.

Such automation is critical for efficient and error-free deployments, especially in agile development environments.

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