Solr 9 was released on May 12th, using the eclipse-temurin:17-jre base image. Thus, we are pinned to Java 17 and Solr's Docker image will thus always use an updated Java 17 version. If you pull the docker image from time to time that is.
However, the base image tag 17-jre did not give us pinning to a specific Ubuntu Linux major release. At the time of Solr 9 release on May 12th it would pull Ubuntu 20.04 (Focal Fossa), but at the end of May, it was auto upgraded to the brand new Ubuntu 22.04 (Jammy Jellyfish). This was not our desire, and we have learnt that due to this, our image is no longer compatible with Docker client versions before 20.10.16. Having a "floating" linux release like this can also break the image in other subtle ways, as well as breaking downstream images using us as a base image. We therefore decided to start pinning not only Java release, but also Linux release in our official Docker images. This means that Solr 9.0 is once again based on Ubuntu 20.04 Focal, i.e. a downgrade. Note that our images will still receive important Linux bug fixes from time to time, but you won't get them unless you re-pull the image. When we upgrade Linux major version in the future, it will be a deliberate decision and not by accident. Read this news on the web page: https://solr.apache.org/news.html#solr-docker-images-now-pin-the-linux-release
