initial commit, here be dragons

roles/docker/files/docker-prune.service

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+[Unit]
+Description=Docker Housekeeping
+
+[Service]
+Type=oneshot
+Nice=19
+IOSchedulingClass=2
+IOSchedulingPriority=7
+ExecStart=/usr/local/bin/docker-prune.sh

roles/docker/files/docker-prune.sh

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+#!/bin/sh
+
+# prune *all* images not currently used
+docker image prune -af
+# prune unused volumes (we keep all state host-mounts)
+docker volume prune -f
+# prune images, containers, networks etc. but keep potentially used one (no -a)
+docker system prune -f
+# update left-over images
+docker images | grep -v "^REPO" | grep -v "^<none>" | sed 's/ \+/:/g' | cut -d: -f1,2 | xargs -L1 docker pull

roles/docker/files/docker-prune.timer

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+[Timer]
+OnCalendar=Mon 12:04