Fixing CF: "Hey, how come ColdFusion debugging output is not showing up in my localhost testing?"
Note: This blog post is from 2018. Some content may be outdated--though not necessarily. Same with links and subsequent comments from myself or others. Corrections are welcome, in the comments. And I may revise the content as necessary.This is a problem that has troubled many CF users for some years (especially as they have moved to later operating systems): they find that ColdFusion debugging output does NOT appear to them when testing using a URL with "localhost" for the domain name but it DOES appear if they use the 127.0.0.1 ip address instead.
TLDR (and update since initial post):
If you can add ::1 to the list of debugging IP addresses in the CF Admin, that should solve this problem. If you cannot, that problem was fixed a few months after I wrote this, in CF2018 update 2 and CF2016 update 8, released in Feb 2019 (and it's no longer a problem on CF2021 and above, of course). For those not yet running those, if you find that adding ::1 just turns into 0:0:0:0:0:0:0:1, read on.
For more on the matter, including why it happened, solving it, etc., read on.