renovate/lib/versioning/docker

Docker doesn't really have versioning, instead it supports "tags" and these are usually used by Docker image authors as a form of versioning.

This Docker versioning implementation in Renovate is designed to handle the most common conventions used in tagging images. In particular, it treats the text after the first hyphen as a type of platform/compatibility indicator.

For example, many images include images with the "-alpine" suffix, e.g. the official node Docker image includes tags like 12.15.0-alpine which is not compatible with 12.15.0 or 12.15.0-stretch. This means users only want/expect upgrades to 12.16.0-alpine and not 12.16.0 or 12.16.0-stretch.

Similarly, a user with 12.14 expects to be upgraded to 12.15 and not 12.15.0.

What type of versioning is used?

It's pretty "wild west" for tagging and not always compliant with SemVer. Docker versioning in Renovate should do a best effort to accept and sort SemVer-like versions.

Are ranges supported?

No. Although a tag like 12.15 might seem like it means 12.15.x, it is a tag of its own and may or may not point to an of the available 12.15.x tags, including 12.15.0.

Are commit hashes supported?

No. An image tag that looks like a Git commit hash should be ignored by Renovate.