Run docker-compose build in .gitlab-ci.yml

Docker also provides an official image: docker/compose

This is the ideal solution if you don't want to install it every pipeline.

Note that in the latest version of GitLab CI/Docker you will likely need to give privileged access to your GitLab CI Runner and configure/disable TLS. See Use docker-in-docker workflow with Docker executor

variables:
  DOCKER_HOST: tcp://docker:2375/
  DOCKER_DRIVER: overlay2

# Official docker compose image.
image:
  name: docker/compose:latest

services:
  - docker:dind

before_script:
  - docker version
  - docker-compose version

build:
  stage: build
  script:
    - docker-compose down
    - docker-compose build
    - docker-compose up tester-image

---

Note that in versions of docker-compose earlier than 1.25:

Since the image uses docker-compose-entrypoint.sh as entrypoint you'll need to override it back to /bin/sh -c in your .gitlab-ci.yml. Otherwise your pipeline will fail with No such command: sh

    image:
      name: docker/compose:latest
      entrypoint: ["/bin/sh", "-c"]

Following the official documentation:

# .gitlab-ci.yml
image: docker
services:
  - docker:dind    
build:
  script:
    - apk add --no-cache docker-compose
    - docker-compose up -d

Sample docker-compose.yml:

version: "3.7"
services:
  foo:
    image: alpine
    command: sleep 3
  bar:
    image: alpine
    command: sleep 3

We personally do not follow this flow anymore, because you loose control about the running containers and they might end up running endless. This is because of the docker-in-docker executor. We developed a python-script as a workaround to kill all old containers in our CI, which can be found here. But I do not suggest to start containers like this anymore.