Issues such as T285875 are difficult to investigate. It's hard to identify the source of responses when we add a custom error page in Varnish if the origin server returned an error (4xx or 5xx does not matter) with no response body. Those responses are indistinguishable from Varnish errors.
We should preserve the value of the Server response header in this sort of situation if possible, or add another header (eg: X-Original-Sever) otherwise.
Change 702648 had a related patch set uploaded (by Ema; author: Ema):
[operations/puppet@production] varnish: Server response header in custom error pages
Change 702671 had a related patch set uploaded (by Ema; author: Ema):
[operations/puppet@production] varnish: do not set reason for 428, 429, 431 and 511
Change 702671 merged by Ema:
[operations/puppet@production] varnish: do not set reason for 428, 429, 431 and 511
The swap of Traffic for Traffic-Icebox in this ticket's set of tags was based on a bulk action for all tickets that aren't are neither part of our current planned work nor clearly a recent, higher-priority emergent issue. This is simply one step in a larger task cleanup effort. Further triage of these tickets (and especially, organizing future potential project ideas from them into a new medium) will occur afterwards! For more detail, have a look at the extended explanation on the main page of Traffic-Icebox . Thank you!