WatchTower is described as 'With watchtower you can update the running version of your containerized app simply by pushing a new image to the Docker Hub or your own image registry' and is an app in the development category. There are four alternatives to WatchTower for a variety of platforms, including Mac, Linux, Self-Hosted, FreeBSD and Docker apps. The best WatchTower alternative is Diun, which is both free and Open Source. Other great apps like WatchTower are dockcheck, What's Up Docker and Tugtainer.
Diun is a CLI application written in Go to receive notifications when a Docker image is updated on a Docker registry. With Go, this app can be used across many platforms and architectures. This support includes Linux, FreeBSD, macOS and Windows on architectures like amd64, i386...
Simplicity. It's a beautiful script. Very elegant for simple local deployments, no annoying dashboards and remotes to study and configure (WUD). It looks like a solid project. Is actively maintained, has some history, multiple contributors and only a few of open issues.
Gets you notified when new versions of your Docker containers are available and lets you react the way you want.
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I don't see a container auto update feature. Just monitoring.