Multiple thumbnails seems to be failing with unexpected 429 return code
* https://upload.wikimedia.org/wikipedia/commons/thumb/5/5d/David_Wilmot.png/250px-David_Wilmot.png
* https://upload.wikimedia.org/wikipedia/commons/thumb/3/34/PAN_Logo.svg/40px-PAN_Logo.svg.png
* https://upload.wikimedia.org/wikipedia/commons/thumb/4/47/British_Punjab_1909.svg/250px-British_Punjab_1909.svg.png
* https://upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Pierre_de_Fermat.png/250px-Pierre_de_Fermat.png
* https://upload.wikimedia.org/wikipedia/commons/thumb/e/eb/Map_at_deutschfeistritz.png/250px-Map_at_deutschfeistritz.png
(and many more, but I suspect this first list gives a good oversight of the issue)
It seems to be similar to https://phabricator.wikimedia.org/T392348 and https://phabricator.wikimedia.org/T307787
While fixing the immediate cause of these 429 errors would be definitely helpful, I would like to have focus as well on the HTTP return code. Returning a 429 error is very detrimental to "bots" like Kiwix scraper which builds offline ZIM archives of Wikimedia projects.
Returned a 5xx error would be way better (or even anything which is not an invitation to retry, most 4xx codes are fine as well).
First because it can only cause more traffic to retry this query (429 is an invitation to retry).
Second because in our specific case we've made the move to a more respectful logic where we try to guess to best interval between queries based on 429 errors returned, but if the upstream begins to send 429 when there is not too much traffic, then we are doomed.