Does a RHEL7 docker container need subscription?
On the Docker hub, you can find some Red Hat docker images , like
https://hub.docker.com/r/richxsl/rhel6.5/
or
https://hub.docker.com/r/lionelman45/rhel7/
but in order to update them, you will need a valid subscription
You will find Red Hat docker images on the Red Hat site, at
https://access.redhat.com/containers
this article summarizes what you need in order to build a Red hat docker image
http://cloudgeekz.com/625/howto-create-a-docker-image-for-rhel.html
it begins with
Pre-requisites
Access to RHEL package repository.
With RHEL 8 Red Hat now offers a universal base image for docker containers which does not require a subscription.