Watchtower Docker on Raspberry Pi — ARM Auto-Updates (Pi 4, Pi 5)

Watchtower ARM Architecture Support

The containrrr/watchtower Docker image is a true multi-architecture image, meaning the same pull command works on x86 servers, Raspberry Pi, Apple Silicon Macs, and AWS Graviton — Docker's manifest list selects the correct architecture automatically.

Prerequisites for Raspberry Pi

• Raspberry Pi 4 or Pi 5 (recommended), Pi 3 also supported
• Raspberry Pi OS (64-bit) or Ubuntu 22.04/24.04 for ARM
• Docker installed (see below)
• At least 1GB RAM on the Pi (Pi 4 2GB+ recommended if running many containers)

Install Docker on Raspberry Pi

# Official Docker install script (works on Pi OS and Ubuntu ARM)
curl -fsSL https://get.docker.com | sh

# Add pi user to docker group
sudo usermod -aG docker pi
# (Or replace 'pi' with your username)

# Log out and back in for group change to take effect
# Verify:
docker --version
docker run --rm hello-world

Install Watchtower on Raspberry Pi

Installation is identical to any Linux host — Docker automatically pulls the ARM image:

# Quick install (Docker Run)
docker run -d \
  --name watchtower \
  --restart unless-stopped \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -v /etc/localtime:/etc/localtime:ro \
  -e WATCHTOWER_CLEANUP=true \
  -e WATCHTOWER_POLL_INTERVAL=86400 \
  containrrr/watchtower

# Verify the correct architecture was pulled:
docker inspect watchtower | grep -i arch
# Should show: "Architecture": "arm64" or "arm"

Docker Compose on Raspberry Pi

# watchtower-compose.yml
version: "3.8"
services:
  watchtower:
    image: containrrr/watchtower
    container_name: watchtower
    restart: unless-stopped
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
      - /etc/localtime:/etc/localtime:ro
    environment:
      # Daily update at 3 AM (conserves Pi's SD card write cycles)
      - WATCHTOWER_SCHEDULE=0 0 3 * * *

      # Remove old images (important on Pi's limited storage)
      - WATCHTOWER_CLEANUP=true

      # Update one container at a time (gentler on Pi's limited RAM)
      - WATCHTOWER_ROLLING_RESTART=true

      # Notification (optional)
      - WATCHTOWER_NOTIFICATION_URL=telegram://TOKEN@telegram?channels=CHAT_ID

Raspberry Pi-Specific Considerations

Memory Constraints

Watchtower itself uses very little memory — typically 15–30 MB RAM. However, pulling large Docker images on a Pi can temporarily spike memory usage. If your Pi has only 1GB RAM:

# Reduce simultaneous operations with rolling restart
- WATCHTOWER_ROLLING_RESTART=true

# Increase stop timeout to prevent force-kills on resource-constrained Pi
- WATCHTOWER_TIMEOUT=60s

ARM Image Availability Check

Not all Docker images on Docker Hub have ARM variants. Before running a container on Pi, verify ARM support:

# Check if an image supports your Pi's architecture:
docker manifest inspect myimage:latest | grep -A2 '"architecture"'

# Or simply try pulling — if no ARM image exists, you'll see:
# "no matching manifest for linux/arm64/v8 in the manifest list entries"

# Watchtower will log pull errors for images without ARM support
# but will continue updating all other containers normally

Common Pi Homelab Stack with Watchtower

version: "3.8"
services:
  # Pi-hole (DNS ad-blocking) — has ARM image
  pihole:
    image: pihole/pihole
    labels:
      - "com.centurylinklabs.watchtower.enable=true"

  # Home Assistant — has ARM image
  homeassistant:
    image: homeassistant/home-assistant
    labels:
      - "com.centurylinklabs.watchtower.enable=true"

  # Vaultwarden — has ARM image
  vaultwarden:
    image: vaultwarden/server
    labels:
      - "com.centurylinklabs.watchtower.enable=true"

  # Watchtower — manages all above
  watchtower:
    image: containrrr/watchtower
    restart: unless-stopped
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    environment:
      - WATCHTOWER_CLEANUP=true
      - WATCHTOWER_LABEL_ENABLE=true
      - WATCHTOWER_SCHEDULE=0 0 4 * * *

Troubleshooting on Raspberry Pi

Error: "exec format error"

# This means you pulled an x86 image on ARM (or vice versa)
# Fix: ensure the image has an ARM variant and re-pull
docker pull containrrr/watchtower  # Will auto-select ARM
docker inspect containrrr/watchtower | grep Architecture

Watchtower using too much CPU during checks

# Reduce check frequency — Pi doesn't need hourly checks
- WATCHTOWER_POLL_INTERVAL=86400   # Once per day
# OR use cron schedule for off-peak hours:
- WATCHTOWER_SCHEDULE=0 0 3 * * *  # 3 AM