Simple script to watch an image on Docker Hub. If the digest changes an email is triggered to notify about the new image.
This is a minimal bash script. It could be extended with authentication or to take action other than sending an email. However, this state is the bare minimum currently needed. Pull requests welcome, feature requests will go unanswered on this one.
Setup a cron job or systemd timer to periodically call the script. The environment variables DOCKER_REPOSITORY, DOCKER_IMAGE, and DOCKER_IMAGE_TAG can be used to configure the image to watch (defaults to drupal:latest). In DOCKER_IW_RECIPIENT you can configure the email recipient (defaults to root). Note that your sendmail console tool must be configured properly to be able to send emails.
The script stores the last know digest in a stamp file. It can be set using the STAMP_FILE environment variable.
The script can send a list of differences between the old and the new image using container-diff. In order for this to work, install container-diff on your machine and set ENABLE_DIFF to a non-empty value.