on RHEL7 docker is available in the extras channel, we can see that it is disabled
[sean@localhost ~]$ subscription-manager repos --list | grep -i extras
Password:
Repo ID: rhel-7-server-extras-rpms
Repo Name: Red Hat Enterprise Linux 7 Server - Extras (RPMs)
Repo URL: https://cdn.redhat.com/content/dist/rhel/server/7/7Server/$basearch/extras/os
Repo ID: rhel-7-server-extras-source-rpms
Repo Name: Red Hat Enterprise Linux 7 Server - Extras (Source RPMs)