The nightly prune ran `docker system prune -a`, which deletes every image no local container uses, so each swarm node kept only its own tasks' images. When the other node failed or was drained, its services had to pull first: on 2026-10-25 Traefik took 11.5 min to start on Docker03. maintenance/swarm_prune.yml (built in) prunes stopped containers, unused networks, dangling images and build cache, then removes only the images that no container uses and no swarm service is pinned to, wherever that service runs. Old digests left by redeploys still go. - A container's image is kept by its id and by the reference it was made from, since on the containerd store the id alone hasn't held a tag. - A node that can't list the swarm's services removes no images and fails rather than pruning blind. - Check mode lists what would go. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>