What are we building?

Not a tool, but update discipline for your entire Docker stack. By the end you have: pinned versions (never latest again), an update notifier (Diun) that tells you when something new is available, a safe rollout routine with a backup beforehand and a rollback plan – and a cleanup rhythm so old images don’t clutter your disk. Tested with Diun v4.33.0 on Docker 29 / Compose v5.3.

The guiding idea is deliberately not “update everything automatically”. With stateful apps (databases, Nextcloud, Immich) an unattended update in the middle of the night can trigger a migration that goes wrong – and nobody is there. The safe way is: pin → get notified → apply deliberately → verify. We treat blind auto-updates honestly at the end (step 6): they have their place, but a small one.

Prerequisites

• Basic knowledge of Docker Compose – you should be able to read tags, volumes and compose.yaml.
• A running stack you want to maintain (e.g. the apps behind your reverse proxy).
• A working backup strategy with Restic – it’s the safety net that makes updates relaxed in the first place.

Step by step

Step 1: Never latest again – pin versions deliberately

The most common mistake appears in countless guides: image: nextcloud:latest. The problem: latest is a moving target. A docker compose pull can pull you a new major version with breaking changes at any time, unasked – you never know what you’re running, and a rollback is barely possible.

Pin every service to a fixed tag instead. Two sensible levels:

• Major tag (postgres:18, nextcloud:34-apache): automatically gets patch and minor updates of the same major version on the next pull, but never a major jump. A good compromise for most services.
• Exact version (vaultwarden/server:1.37.1): full control, nothing changes without your involvement. Ideal for delicate, stateful apps.

What you’re running right now is shown by Compose per project:

cd ~/YOUR_APP && docker compose images

CONTAINER           REPOSITORY          TAG                 PLATFORM            IMAGE ID            SIZE                CREATED
diun-demo-whoami    traefik/whoami      v1.11.0             linux/amd64         200689790a0a        3.04MB              17 months ago

If latest appears anywhere in the TAG column, that’s your first candidate to pin. Enter the specific tag into the compose.yaml – that’s the foundation for everything else.

Which version is currently stable you look up at the source, not by gut feeling: the tags overview on Docker Hub (or GHCR) of the image, or the release notes on GitHub. For official images this also works via API:

curl -s "https://hub.docker.com/v2/repositories/library/postgres/tags/?page_size=20" | grep -oE '"name":"[0-9.]+"'

Take the highest stable version of the same series you want to run – pre-releases (rc, beta) stay out.

Step 2: See what’s outdated – the update notifier Diun

Pinning means updates no longer come on their own. So you need someone to let you know when a new image is available. That’s exactly what Diun (Docker Image Update Notifier) does – it updates nothing, it only watches and notifies. Give it its own folder:

mkdir -p ~/diun && cd ~/diun

The compose.yaml:

services:
  diun:
    image: crazymax/diun:4.33.0
    command: serve
    environment:
      - "TZ=Europe/Berlin"
      - "DIUN_WATCH_SCHEDULE=0 8 * * *"          # daily at 8 a.m.
      - "DIUN_PROVIDERS_DOCKER=true"
      - "DIUN_PROVIDERS_DOCKER_WATCHBYDEFAULT=false"
    volumes:
      - ./data:/data
      - /var/run/docker.sock:/var/run/docker.sock:ro
    restart: unless-stopped

• DIUN_PROVIDERS_DOCKER=true lets Diun discover your running containers via the Docker socket.
• WATCHBYDEFAULT=false means Diun only watches containers you explicitly mark – so you don’t get a flood about things that don’t interest you.
• DIUN_WATCH_SCHEDULE is a cron expression; once a day is plenty and spares the registry rate limits.

Mark the containers Diun should keep an eye on via a label in their compose.yaml:

    labels:
      - "diun.enable=true"
      - "diun.watch_repo=true"

diun.enable=true switches on monitoring. diun.watch_repo=true lets Diun search the whole repository for newer tags (e.g. whether a 19 already exists for your postgres:18) – without this label, Diun only checks whether your exact tag got a new image. Start Diun and watch the first run:

docker compose up -d && docker compose logs -f diun

INF Found 1 image(s) to analyze provider=docker
INF New image found      image=docker.io/traefik/whoami:v1.11.0 provider=docker
INF New image found      image=docker.io/traefik/whoami:v1.12.0 provider=docker
INF New image found      image=docker.io/traefik/whoami:latest-arm64 provider=docker
INF Jobs completed       added=97 failed=0 skipped=0 unchanged=0 updated=0

The first run is just the inventory: Diun writes every tag it finds into its database as “New image found” (added). That one watched container yields 97 entries is down to watch_repo – Diun then fetches the manifest for every tag in the repository, including architecture variants like latest-arm64 or v1.10.0-armv7.

Two things follow from this that are easy to get wrong:

• The first run does not notify. The option watch.firstCheckNotif defaults to false, and that applies per image tag. Everything Diun sees for the first time lands in the database silently. It only reports once something changes later on.

• watch_repo costs registry requests. 97 manifest queries per run almost blow the Docker Hub limit without a login (100 requests per IPv4 address or IPv6 /64 subnet) on their own. On the second run of the same day our test ran straight into it – StatusCode: 429 and failed=36 in the log. How much budget is left – and which window the registry is currently counting in – it tells you itself:

  Terminal

  TOKEN=$(curl -s "https://auth.docker.io/token?service=registry.docker.io&scope=repository:ratelimitpreview/test:pull" | cut -d'"' -f4)
  curl -sI -H "Authorization: Bearer $TOKEN" https://registry-1.docker.io/v2/ratelimitpreview/test/manifests/latest | grep -i "^ratelimit"

  Ausgabe

  ratelimit-limit: 100;w=3600
  ratelimit-remaining: 98;w=3600

  w is the window width in seconds. Docker documents a six-hour window; our test VPS consistently got w=3600, i.e. one hour, in August 2026. So rely on the header rather than on a remembered number – and note that this query itself costs a request. Beyond that, narrow the tags down to what you actually care about – real release tags:

    labels:
      - "diun.enable=true"
      - "diun.watch_repo=true"
      - "diun.include_tags=^v1\\.1[12]\\.\\d+$$"
      - "diun.sort_tags=semver"

include_tags is a regular expression. Two pitfalls hide in the notation: the backslashes have to be doubled in YAML, and the trailing $ is written as $$ – otherwise Compose tries to substitute an environment variable. With this label, exactly the two real release tags remain out of the 97 entries:

INF Found 1 image(s) to analyze provider=docker
INF New image found      image=docker.io/traefik/whoami:v1.11.0 provider=docker
INF New image found      image=docker.io/traefik/whoami:v1.12.0 provider=docker
INF Jobs completed       added=2 failed=0 skipped=0 unchanged=0 updated=0

So that the notice doesn’t just sit in the log, you attach a notification. Diun can do email, Telegram, ntfy, Gotify and many more. For Telegram – you may already have set up the bot in the Uptime Kuma tutorial – two lines in the environment block are enough:

      - "DIUN_NOTIF_TELEGRAM_TOKEN=YOUR_BOT_TOKEN"
      - "DIUN_NOTIF_TELEGRAM_CHATIDS=YOUR_CHAT_ID"

All other channels are in the Diun documentation. This is what the notice looks like – here via ntfy in the browser, as soon as a newer version appears for one of your pinned images:

Step 3: Apply an update safely (the routine)

Diun reports an update – now comes the actual discipline. Never just pull blindly. The fixed order for every service:

1. Read the release notes. On a major jump (e.g. Nextcloud 34 → 35) this is mandatory: are there breaking changes, migration steps, removed options? Two minutes here save hours of debugging.

2. Back up first. An update is the classic moment for something to break. Make a Restic backup of the data (for big jumps, additionally a netcup snapshot). Then a failure is only a setback, not data loss.

3. Bump the tag and pull. Set the new tag in the compose.yaml and fetch the image:

docker compose pull

 Image traefik/whoami:v1.12.0 Pulled

4. Restart. Compose only replaces the affected container, the volumes stay:

docker compose up -d

 Container diun-demo-whoami Recreated
 Container diun-demo-whoami Started

5. Verify. Does the container run cleanly (docker compose ps, docker compose logs), and does the app still do what it should? Stateful apps may now run a database migration – take a look at the log until it’s through.

6. Have a rollback in mind. If something goes wrong, set the tag in the compose.yaml back to the old version and do docker compose up -d again. Because your data lives in the volume (not in the container), for most apps this is a clean step back. Only if the new version has already migrated the database does a tag rollback no longer help – then you need the backup from step 2. That’s exactly what it’s for.

Step 4: Don’t forget the base – host, engine, hidden images

Your apps are only half the battle. Equally important:

• Operating system & Docker engine. The OS and security packages of Debian you best install automatically with unattended-upgrades. The Docker engine is deliberately left out of that: unattended-upgrades by default only pulls the Debian sources (origin=Debian), not the Docker APT repo (origin=Docker, download.docker.com). So the engine isn’t updated in the background and won’t unexpectedly restart all your containers at night – because an engine update briefly takes running containers down. You’d better determine that moment yourself and update the engine specifically by hand when it fits:

  Terminal

  sudo apt update && sudo apt upgrade docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

  Afterwards check with docker compose ps that all stacks are up again.

  If a brief container restart at night doesn’t bother you, you can also let the engine come along with unattended-upgrades: allow the Docker repo in /etc/apt/apt.conf.d/50unattended-upgrades as an additional origins pattern. What matters is archive= – the Docker repo sets no Codename field, the often-recommended codename=${distro_codename} would run into the void and Docker would stay out despite the entry:

  Ausgabe

  "origin=Docker,archive=${distro_codename}";

• Hidden images. Many stacks contain databases, caches and helper services (postgres, redis, mariadb, gotenberg …) that nobody thinks of. Diun watches them automatically as soon as the respective container carries the diun.enable label – so give it to all long-lived services, not just the visible main app.

• Extensions of your reverse proxy. Pinned plugin versions too (e.g. the CrowdSec bouncer) or Traefik itself want to be updated deliberately.

Step 5: Clean up – reclaim storage

Every update leaves the old image behind. After a few months this adds up. What you’re using is shown by:

docker system df

TYPE            TOTAL     ACTIVE    SIZE      RECLAIMABLE
Images          26        4         14.75GB   14.16GB (95%)
Containers      4         4         45.06kB   0B (0%)
Local Volumes   0         0         0B        0B
Build Cache     36        0         828.2MB   828.2MB

Unused, untagged (“dangling”) images are removed by the safe default command:

docker image prune

Careful: this only removes dangling images. An old, still tagged version (like whoami:v1.11.0 after the update to v1.12.0) doesn’t count as dangling and stays behind. You reclaim that specifically:

docker rmi traefik/whoami:v1.11.0

Untagged: traefik/whoami:v1.11.0
Deleted: sha256:200689790a0a0ea48ca45992e0450bc26ccab5307375b41c84dfc4f2475937ab

Whoever wants to clean up more radically uses docker image prune -a (removes all images no running container currently uses). That’s powerful, but pulls everything anew on the next start – use it deliberately, not in cron.

The safe docker image prune -f (dangling only), on the other hand, you can run regularly without worry – e.g. weekly via a systemd timer or cron. That way no junk piles up between your update sessions in the first place, and you reclaim the storage automatically.

Step 6: Auto-update – when it’s okay (and when not)

The question remains: why not everything fully automatic? The best-known tool for that is Watchtower – it pulls new images and restarts containers on its own. Two catches:

• The upstream is orphaned. The official containrrr/watchtower hasn’t had a release since v1.7.1 (2023-11-11) – and the repository was archived at the end of 2025 (2025-12-17), i.e. mothballed for good. Whoever uses it better reaches for a maintained fork like nickfedor/watchtower.
• Auto-update is dangerous for stateful apps. Lifting a database or Nextcloud over a major jump unattended at night is the opposite of “safe”.

Auto-update makes sense at most for uncritical, stateless services – and even then rather in monitor mode (WATCHTOWER_MONITOR_ONLY=true), which only reports instead of updating. For everything else, the deliberate routine from step 3 beats any automation tool. That’s exactly why Diun (notify) + manual update is the recommendation here, not Watchtower (act).

When things go wrong

Maintenance & backups

• The rhythm. Diun reports → you read the release notes → backup → update → verify. In practice that’s a manageable appointment once a month; critical security holes you patch immediately. Honestly: safe self-hosting doesn’t work entirely without manual work – but 15 minutes a month is the deal.
• Fast movers first. Some projects release frequently and with breaking changes – Immich, mailcow, CrowdSec, Grafana and Nextcloud. Those you look at first and more often, quiet candidates (databases, Redis) less so.
• Backups are the core of this recipe. An update without a backup is a gamble; with Restic at your back, every update becomes relaxed. Before big jumps, additionally a snapshot – it brings the whole server back in one go.
• Version your compose.yaml files. Whoever keeps their Compose files in a Git repo can roll back not only data but also the configuration to any earlier state – and sees in the history exactly which tag was bumped when.
• Keep the tools up to date too. Diun itself and your reverse-proxy plugins belong in the update round as well – otherwise the maintainer doesn’t maintain itself.