Resolve "How to handle breaking external links?"

Related to #364 (closed)

_posts/2019/12/2019-12-20-Welcome-Post.md

@@ -108,10 +108,10 @@ trainings, events and services in 2020 and forward.
 [hip-link]: https://www.helmholtz.de/en/research/information-data-science/helmholtz-imaging-platform-hip/
 [dlr]: https://dlr.de/sc
 [dkfz]: https://www.dkfz.de/
-[gfz]: https://www.gfz-potsdam.de/zentrum/escience-zentrum/ueberblick/
+[gfz]: https://www.gfz-potsdam.de/sektion/escience-zentrum/ueberblick
 [hzdr]: https://www.hzdr.de/
 [ufz]: https://www.ufz.de/
 [contributing]: https://gitlab.hzdr.de/hifis/software.hifis.net/blob/master/CONTRIBUTING.md
-[cloud-link]: https://www.hifis.net/mission/cluster-cloud.html
-[backbone-link]: https://www.hifis.net/mission/cluster-backbone.html
+[cloud-link]: {% link services/cloud/Helmholtz_cloud.md %}
+[backbone-link]: {% link services/backbone-overview.md %}
 [gitlab-project]: https://gitlab.hzdr.de/hifis/software.hifis.net