Return latest if no upstream registry is available

[aapjeisbaas]

Describe the problem to be solved

Applicable when running a portable cluster with an unpredictable or no internet connection.
I have a few pods that are defined as image:latest without the pull policy IfNotPresent

If you start a pod with a latest tag it will always try to pull from a registry.
Spegel will try to fetch this upstream and fails with a timeout.
The pod can't start even though there is a cached image available.
Ending in a ErrImagePull > ImagePullBackOff

Extra info:
I run spegel in K3s with --embedded-registry in thje install command.
I have a registries.yaml:

mirrors:
  "*":

spegel metrics:

[root@localhost ~]# kubectl get --raw /api/v1/nodes/localhost/proxy/metrics | grep -F 'spegel'
# HELP spegel_advertised_image_digests Number of image digests advertised to be available.
# TYPE spegel_advertised_image_digests gauge
spegel_advertised_image_digests{registry="docker.io"} 17
spegel_advertised_image_digests{registry="ghcr.io"} 1
spegel_advertised_image_digests{registry="quay.io"} 6
spegel_advertised_image_digests{registry="registry.gitlab.com"} 1
# HELP spegel_advertised_image_tags Number of image tags advertised to be available.
# TYPE spegel_advertised_image_tags gauge
spegel_advertised_image_tags{registry="docker.io"} 22
spegel_advertised_image_tags{registry="ghcr.io"} 1
spegel_advertised_image_tags{registry="quay.io"} 6
spegel_advertised_image_tags{registry="registry.gitlab.com"} 5
# HELP spegel_advertised_images Number of images advertised to be available.
# TYPE spegel_advertised_images gauge
spegel_advertised_images{registry="docker.io"} 39
spegel_advertised_images{registry="ghcr.io"} 2
spegel_advertised_images{registry="quay.io"} 12
spegel_advertised_images{registry="registry.gitlab.com"} 6
# HELP spegel_advertised_keys Number of keys advertised to be available.
# TYPE spegel_advertised_keys gauge
spegel_advertised_keys{registry="docker.io"} 175
spegel_advertised_keys{registry="ghcr.io"} 18
spegel_advertised_keys{registry="quay.io"} 107
spegel_advertised_keys{registry="registry.gitlab.com"} 31
# HELP spegel_mirror_requests_total Total number of mirror requests.
# TYPE spegel_mirror_requests_total counter
spegel_mirror_requests_total{cache="miss",registry="registry.gitlab.com",source="internal"} 6

Proposed solution to the problem

In this scenario I would love it if Spegel would respond with the latest image from cache.

[phillebaba]

The embedded k3s version of Spegel works slightly differently. Have you enabled resolving latest tags?

https://docs.k3s.io/installation/registry-mirror#latest-tag

I also reccomend reading the FAQ about using latest tag with Spegel.

https://github.com/spegel-org/spegel/blob/main/docs/FAQ.md#why-am-i-not-able-to-pull-the-new-version-of-my-tagged-image