I was testing some things out in Katello when I hit this when I tried to pull a docker repo:
❯❯❯ docker pull localhost:5000/default_organization-library-redisv-Tester-redis:latest
2015/03/01 15:08:15 Invalid repository name (default_organization-library-redisv-Tester-redis), only [a-z0-9-_.] are allowed
Looks like Docker repo names could only be 30 characters in docker-1.3.2-4.el7.centos.x86_64 (which is the version I have on centos7):
Since this issue was entered in Red Hat Bugzilla, the release flag has been
set to ? to ensure that it is properly evaluated for this release.