GitLab Cloud - How to use my own Docker Image

I am trying to use a custom docker image which offers the support for the Android emulator.

I am using a GitLab runner in Kubernetes.

I tried to connect to the docker registry offered by GitLab but I had the message:

Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

My question is, is Docker Registry available only when the GitLab Runner is running a CI job?

I found my problem. docker was not running when I typed the docker login command.