Argus is a lightweight monitor to notify of new software releases via Gotify/Slack/other messages and/or WebHooks.
Take a look at Argus. I use it to monitor the application version (not a container tag). I get notifications via mailrise (SMTP gateway for apprise) which then go to Gotify and Discord. I have webhooks setup to run scripts so I can approve the update from the Argus app to automate the update. You can also have it set to auto approve.
Receive notifications when an image is updated on a Docker registry
https://crazymax.dev/diun/ could check for new containers for you
Collect and Analyze Billions of Data Points in Real Time. Manage all types of time series data in a single, purpose-built database. Run at any scale in any environment in the cloud, on-premises, or at the edge.
Universal dependency update tool that fits into your workflows.
https://github.com/renovatebot/renovate or https://github.com/dependabot if you using git for your configuration
Work with remote images registries - retrieving information, images, signing content
You could try some commandline tool like skopeo to fetch the image tags regularly and do some shell magic to notify you on any change you want
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