How to use docker-compose in GitLab CI

.gitlab-ci.yml

# Using edge-git ensures we're always pulling the latest
# You can lock into a specific version using the *-git tags
# on https://hub.docker.com/_/docker/
image: docker:edge-git
services:
- docker:dind

# If you only need compose in a specific step definitely put this
# only in that step so it's not executed unnecessarily
before_script:
  - apk add --no-cache py2-pip && pip install docker-compose