What is Shephard?

Features:

A Docker swarm service for automatically updating your services whenever their base image is refreshed.

How does it work?

Shepherd just triggers updates by updating the image specification for each service, removing the current digest.

Most of the work is thankfully done by Docker which resolves the image tag, checks the registry for a newer version, and updates running container tasks as needed.

Also, Docker handles all the work of applying rolling updates. So at least with replicated services, there should be no noticeable downtime.