Manually check whether an image is out of date

[SimeonEhrig]

Hello,

I have a special case to update a container. If I update a Nextcloud container, a new image is downloaded. When the new image is starting, it will check the container version and the version of the Nextcloud installation, which is stored in a persistent volume. If the installation is older than the container version it will automatically update the installation. An updated installation cannot be rolled back.

Therefore, if the container fails to start after the container update, but already started the update process of the installation (maybe this process has a problem), Podman will automatically roll back the container, the old container will start and fail because a container with an older Nextcloud version cannot run with an installation of a newer version. So the roll back is also broken.

I solve the problem with following approach. During the backup process I do the following stuff:

1. create a backup
2. check for a new image by a hand-written, a little bit in-stable script
3. if the there is a new image, tag the current image and the backup with special tags, that I know how to restore the backup
4. upgrade the image manually

The problem is the handwritten script for checking new images. Podman has already the mechanism. Therefore it would be cool if I could use the mechanism e.g. podman check-update <image_name>.

Does somebody know if this is already possible?

A workaround would be to create an quadlet with a Nextcloud image and the auto update property and then run podman auto-update --dry-run but the start up time for a new Nextcloud container takes a while, because it does download a whole Nextcloud installation.