Repo maintainers can trigger the build of a specific version via GitLab API
curl -X POST \
-F token=${GITLAB_YII2_DOCKER_TOKEN} \
-F ref=master \
-F "variables[DOCKERFILE_FLAVOUR]=debian" \
-F "variables[PHP_BASE_IMAGE_VERSION]=7.1.3-apache" \
-F "variables[TEST_YII_VERSION]=2.0.11" \
https://gitlab.com/api/v4/projects/2858803/trigger/pipeline
This can also be used to test pre-releases of PHP or other flavors, if there is a Dockerfile available for them.
Tokens are managed under GitLab settings.