I've merged (what I think are) the final patches required for using custom/vanity domains with the Cloud VPS web proxy. Here is an example:
https://wmcs-proxy-test.taavivaananen.fi/
And administrator documentation is available at [0]. [1] is the task tracking the implementation of this.
[0]: https://wikitech.wikimedia.org/wiki/Portal:Cloud_VPS/Admin/Web_proxy#Enable_... [1]: https://phabricator.wikimedia.org/T342398
I have not yet documented this in the user-facing docs, because we first need to decide which projects can use this feature. Historically the use of custom domains for Cloud VPS projects has been restricted by the fact that those required a floating IPv4 and we don't have many of those. My feeling (but I haven't checked) is that the vast majority of granted requests from the time I've been here have been for affiliates and for projects that are migrating from some external hosting with an existing domain to Cloud VPS.
Now that IPv4 scarcity is no longer a factor in this, we could in theory set up custom domains for everyone that wants one. Are we willing to do this or do we want to keep some requirements for having one? In my head the biggest argument for encouraging/requiring use of *.wmcloud.org is that it removes a major SPOF possibility from individual maintainers having control of vanity domains and then disappearing leaving the project stuck.
Taavi