dtm

README

Docker Tag Monitor (dtm)

Purpose

The overall goal is to prune older versioned images/tags, and keep only the leading edge.

Specifically, for any given repository/image:

• If there is a latest, keep it
• If there is, e.g. a 1 and a 1.2, keep both, even if they do not point to the same hash
• If there is, e.g. 1 and 1.2 and 1.2.3, keep all, as above
• Remove everything else that doesn't qualify

Usage

If you are using a non-standard container engine (CE) host, i.e. anything that isn't unix:///var/run/docker.sock, then the DOCKER_HOST environment variable needs to be set when running dtm:

export DOCKER_HOST="$(docker context inspect --format="{{ .Endpoints.docker.Host }}")"
dtm

Correctness

Check the output of dtm against docker proper with the following comparison:

delta \
  <(DOCKER_HOST="$(docker context inspect --format="{{ .Endpoints.docker.Host }}")" ./dtm | sort -f) \
  <(docker images --format='table {{ .Repository }}\t{{ .Tag }}\t{{ .ID }}' | tail -n +2 | sort -f)