2020-06-15: Hard deadline. Compatibility period is over and all HTTPS request to the legacy URLs are redirected to the new domain. The legacy tools.wmflabs.org domain is no longer supported for any tools created after this point in time.
In a separate server from the main front proxy, there is an nginx server that loads a LUA script. This script checks if the tool is allowed to have a legacy redirect (we don't want to allow the legacy redirect for newer webservices), by checking a static list.
So we need to set up a new domain (such as tools-redirect.wmflabs.org) to make toollabs: prefix working for all webservices.
(First raised at https://meta.wikimedia.org/wiki/Talk:Interwiki_map#Troubleshooting)