When attempting to pull public images (e.g. python:3.6, node:latest) from Docker, our GitLab runner failed with the following error message:
Running with gitlab-runner 12.2.0 (a987417a)
on GitLab Runner XYZ
Using Docker executor with image python:3.6 ... 00:17
Starting service python:3.6 ...
Pulling docker image python:3.6 ...
ERROR: Preparation failed: Error: No such image: python:3.6 (executor_docker.go:199:0s)