Watchtower is an automated Docker container update tool. It monitors running containers and checks for newer images, automatically updating and restarting containers when a new version is available. This helps maintain up-to-date and secure Docker environments with minimal manual intervention.

Pros

• Automatic updates: Keeps containers up-to-date without manual intervention
• Flexible configuration: Supports various update schedules and notification options
• Secure: Can use private registries and supports authentication
• Easy to set up: Can be run as a Docker container itself

Cons

• Potential downtime: Container restarts may cause brief service interruptions
• Limited control: Automatic updates may introduce unexpected changes or issues
• Resource intensive: Constant checking for updates can consume network and CPU resources
• Dependency conflicts: Updating containers may lead to compatibility issues with other services

Getting Started

To get started with Watchtower, you can run it as a Docker container:

docker run -d \
  --name watchtower \
  -v /var/run/docker.sock:/var/run/docker.sock \
  containrrr/watchtower

This command will start Watchtower in the background, monitoring all running containers and updating them when new images are available.

To customize Watchtower's behavior, you can use environment variables:

docker run -d \
  --name watchtower \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -e WATCHTOWER_POLL_INTERVAL=86400 \
  -e WATCHTOWER_CLEANUP=true \
  containrrr/watchtower

This example sets the polling interval to 24 hours (86400 seconds) and enables cleanup of old images after updates.

For more advanced configurations, you can use a config file:

# /path/to/config.json
{
  "cleanup": true,
  "include-stopped": true,
  "notifications": {
    "slack": {
      "hook_url": "https://hooks.slack.com/services/xxx/yyy/zzz",
      "identifier": "watchtower-server-1"
    }
  }
}

Then run Watchtower with the config file:

docker run -d \
  --name watchtower \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -v /path/to/config.json:/config.json \
  containrrr/watchtower

This setup includes stopped containers in the update process and sends notifications to Slack when updates occur.