Quick note, the existing Let's Encrypt integration does not support Pages. We are working on it, but it's worth noting Pages has multiple modes it can run in.

One is by setting up wildcard domains at the server level, like we have on GitLab.com with gitlab.io. We have an issue open for this, but the primary challenge is that Let's Encrypt requires DNS-01 validation for wildcard certificates, with a new challenge each renewal. That is difficult to automate through our Omnibus package. The issue tracking this work is here: https://gitlab.com/gitlab-org/omnibus-gitlab/issues/3342

The other method allows users bring their own "custom domains": https://docs.gitlab.com/ee/administration/pages/#custom-doma...

This is easier to manage, as we can do HTTP or SNI validation for each domain without hitting LE's rate limits. We are working on this now here: https://gitlab.com/gitlab-org/gitlab-ce/issues/28996