did you delete gitlab ci docker cache?

If you accidentally deleted gitlab ci docker cache or because of space constraints

especially /var/lib/docker/overlay2/ folder then most likely your next ci builds will fail.

when you run ci build, you will come across errors like

ERROR: Failed to create container volume for /builds/xxxx Error: No such image: gitlab/gitlab-runner-helper:x86_64-f100a208 (executor_docker.go:175:0s)
ERROR: Preparation failed: Error: No such image: gitlab/gitlab-runner-helper:x86_64-f100a208 (executor_docker.go:175:0s)

so most probably the reason is, docker database still have info about those containers so it is throwing error.

so solution is,

first prune database

docker system prune -a

if the problem still persists, then restart docker

i.e. sudo systemctl restart docker

then your builds should start working again 🙂