How to use absolot Urls by submodules?

Hallo,everyone. My Boss asked me to use absolute URLs for our submodules,but when I used it and run it in piepeline, it always need an ssh service. I tried to install openssh service in Dockerfile but that didn't work,because "variables: GIT_SUBMODULE_STRATEGY: recursive" always work before my Dockerfile. Why Gitlab didn't support absolut URLs,or if anyone have some good ideas? Thanks.

Ada