GitLab Runner & Docker: ERROR: Preparation failed: Error: No such image

Question

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)

Answer 1

The cause was we exceeded Dockers pull rate limit:

• Free plan – anonymous users: 100 pulls per 6 hours
• Free plan – authenticated users: 200 pulls per 6

How can I check my current rate?

See https://docs.docker.com/docker-hub/download-rate-limit/#how-can-i-check-my-current-rate

How to increase the rate limit?

Authenticate with Docker Hub to increase to 200 pulls per 6 hours:

docker login

Alternatively you can cache Docker images to reduce the number of calls to DockerHub from your CI/CD infrastructure.