URLs like https://docs.wikimedia.org/cover/something currently redirect to https://doc.wikimedia.org, thus losing the path, query or fragment of the link the user navigated to.
Most redirect domains at WMF are transparent redirects that swap the domain but forward the rest of the url.
The alias got setup by T100349 and, If I remember well, the alias docs was directed to the text cache, then to Mediawiki Apache and the redirect handled by those servers with:
funnel docs.wikimedia.org https://doc.wikimedia.org
funnel stands for:
Redirect a whole domain (or set of domains) to a single URL
So doc.wikimedia.org is the canonical URL, and docs is merely a convenience redirect for the rare case when some writes docs.wikimedia.org in the URL bar.
Eventually I found out we have hits recorded since January 4th 2018 in Pivot. Looking at https://turnilo.wikimedia.org/#webrequest_sampled_128 sampled webrequests on pivot:
| URL hosts | Hits |
|---|---|
| doc.wikimedia.org (canonical) | 2071 |
| doc.mediawiki.org (alias) | 1 |
| docs.wikimedia.org (alias) | 1 |
From the two sampled requests we had:
https://doc.mediawiki.org/Parsoid/master/
https://docs.wikimedia.org/core/misc/drupal.js (sounds like a bot scan)