An Open Source alternative to Docker Trusted Registry is Portus from SUSE. This is a front end to a private Open Source registry that allows for fine grained control of registry access and content: it can manage users, teams, and namespaces (no, not the kernel ones). It can integrate with LDAP for authentication and offers an audit trail, and can be extended for security scanning.
For s390x, quite a few options for base images are available on Docker Hub/Docker Store these days. They vary from enterprise environments over community distributions to minimal images. This post gives an overview on what is provided by various sources.
The previous post mentioned that Docker provides CE packages for Ubuntu. For users of Debian, SLES, RHEL, Fedora, ClefOS, openSUSE, and Alpine, there is still an option to get the latest Docker CE version to their environment:
Today, Docker CE v17.06 has been released. It offers a series of enhancements as laid out in their announcement blog post. However, there is one more thing: the release comes with s390x binaries. Out of the three major enterprise distributions supported on the mainframe, Docker offers CE for Ubuntu. Particularly, Docker CE is not provided for SLES and RHEL (on any platform). Accordingly, binaries are available for Ubuntu for IBM z Systems.
(Note: See the next post if your distribution of choice happens to be something else than Ubuntu.)
It's a while since Docker changed their release naming system. In the past, the version looked like 1.xx, with xx counting up. After 1.13, Docker moved to a pattern that is easy to grasp and accommodates various life cycles of free and commercial releases.