GitLab: How to build Docker images in your GitLab CI

This documentation is part of the CI/CD guide. You can view the complete guide here: How to use GitLab CI/CD.

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If your project repository contains Dockerfile files, you can automate the building, running, and, if needed, publishing of your Docker images to a registry.

Step 1: Enable Docker in Docker (DinD) support

To begin, enable "Docker in Docker" (DinD) support from your Stackhero dashboard.

Enabling DinD support presents a security risk, especially if you want to isolate your users and prevent them from accessing each other's projects.

Step 2: Configure the GitLab CI pipeline

Next, update your gitlab-ci.yml file to include a pipeline configuration that builds your Dockerfile using DinD. Here is an example configuration:

image: docker:29

build:
  stage: build
  services:
    - name: docker:29-dind
      alias: docker
  variables:
    # Point the Docker CLI at the Docker-in-Docker service, via its plain
    # (non-TLS) port. See the note below about why DOCKER_HOST matters.
    DOCKER_HOST: "tcp://docker:2375"
    DOCKER_TLS_CERTDIR: ""
  before_script:
    - docker info
  script:
    # Replace "my-docker-image" with the name of your desired image:
    - docker build -t my-docker-image .
    # Optionally, test the Docker image:
    # - docker run my-docker-image /script/to/run/tests

The docker:29-dind service starts a Docker daemon alongside your job, and DOCKER_HOST tells the docker CLI to use it. Always set DOCKER_HOST when you declare a docker:dind service: if you omit it, the CLI silently connects to a different daemon, and your build may succeed even if the service is misconfigured, masking real issues. DOCKER_TLS_CERTDIR: "" allows the use of the plain, non-TLS port 2375 on the internal job network.

As a simpler alternative, you can remove the services block and both variables entirely: Stackhero's runner already exposes a ready-to-use Docker daemon via a mounted socket, so a simple docker build command works immediately.

For more information on building Docker images with GitLab CI, refer to the official GitLab documentation.