Understanding the difference between "image=docker:stable + service=docker-dnd" and "image=docker:stable-dnd"

[mcallaghanbsm (Matt Callaghan (BSM))]

The first example comes from (as per the official example: https://gitlab.com/gitlab-examples/docker/blob/master/.gitlab-ci.yml)

and,

I am seemingly not alone in this question, see: https://stackoverflow.com/questions/47280922/role-of-docker-in-docker-dind-service-in-gitlab-ci