In order for T40: Set up redirects from old bugzilla.wikimedia.org URLs to work, first bugzilla.wikimedia.org needs to point to phabricator.wikimedia.org.
According to @Dzahn, in production things aren't as simple as they were in our wmflabs test:
<mutante> i can't _just_ redirect the DNS
<mutante> because the server phab runs on, doesn't have a public address
<mutante> it is all proxied behind varnish cluster