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So this is a rather strange error. After migrating my websites via Plesk Migrator to my new server (from Ubuntu to Debian), I get a 504 error when trying to access one of my websites. However, once I turn on the old server everything works just fine. Which is strange, because the domain points to the new IP now of course and DNS settings should be fine too (see below). Confusingly enough, all the other websites work just fine

How would you approach this error?

Comparison of DNS settings of the website that is not working and a website that is working (default settings anyway)

Hillcow
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  • Show what you need to show as text inside the question do not put the meat of it in a remote picture. – Patrick Mevzek Jan 09 '18 at 13:17
  • An HTTP 504 error is probably not DNS related. Did you look at your logfiles? – Patrick Mevzek Jan 09 '18 at 13:18
  • @PatrickMevzek I just thought it had to be related to DNS due to the fact the site is working when the old server is running. Yes, but looking at logfiles I did not find anything too interesting, just a bunch of time-outs ("upstream timed out while reading response header from upstream"). Which logs should I look at and what exactly am I looking for? – Hillcow Jan 09 '18 at 14:12
  • So you are using some kind of proxy and the proxy can not reach the upstream but definitively knows it. Check connectivity between the two and check manually contacting the upstream from the proxy with any web client like `curl` or `wget` – Patrick Mevzek Jan 09 '18 at 14:19
  • But that's the thing, I don't want my new server to contact the old one obviously. I have no clue why it would do that. DNS should be fine, config of my forum software only points to localhost for the database. Is there any way to figure out where exactly my server is trying to contact the old one? – Hillcow Jan 09 '18 at 14:29
  • So the new server does not seem to recognize itself and wants to propagate to another ones? Do you have extra stuff in `/etc/hosts` or anything else that could modify the normal name resolution on this new server? Or IPv4/IPv6 setup differences between the two. – Patrick Mevzek Jan 09 '18 at 21:51
  • No extra stuff in `/etc/hosts`. No IPv4/6 differences. I can't think of anything else. I'm using Plesk to manage my websites, but the configuration in there should be fine too. My old server might have been hacked. Is there something you can think of a hacker would do to make sure I don't turn off this server? Also, I tried to narrow down what services I can stop on the old server so that the site on the new server still works, but some services restart automatically. – Hillcow Jan 10 '18 at 00:04
  • I've found the error. – Hillcow Jan 10 '18 at 10:42

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So, this was a tough case. I've spent so many evenings trying different setups, switching operating systems, different DNS settings, etc. - when in the end, this had nothing to do with the server itself. It was a simple script that was fetching a rss feed from another of my websites which I don't run anymore. It's domain still pointed to the old server. With the old server being turned off, the script did not respond whatsoever and that's the timeout.

I've never been so satisfied finding a bug, wooohoo.

Hillcow
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