My domain is:
lingnu.com
I ran this command:
certbot-auto certonly --dry-run --debug-challenges -v --nginx -d lingnu.com
It produced this output:
http-01 challenge for lingnu.com
Reporting to user: The following errors were reported by the server:
Domain: lingnu.com
Type: unauthorized
Detail: Invalid response from http://lingnu.com/.well-known/acme-challenge/jSVVTObWuHMwqm2RtiGvcAQXos6liDfnOf_QvQx7p5s [2a02:c207:2021:373::1]: "<html>\r\n<head><title>404 Not Found</title></head>\r\n<body bgcolor=\"white\">\r\n<center><h1>404 Not Found</h1></center>\r\n<hr><center>"
My web server is (include version):
nginx 1.10.3-1+deb9u2
The operating system my web server runs on is (include version):
Description: Debian GNU/Linux 9.9 (stretch)
Release: 9.9
Codename: stretch
My hosting provider, if applicable, is:
https://contabo.com/
I can login to a root shell on my machine (yes or no, or I don’t know):
Yes
I’m using a control panel to manage my site (no, or provide the name and version of the control panel):
No
The version of my client is (e.g. output of certbot --version or certbot-auto --version if you’re using Certbot):
certbot 0.38.0
Details:
When I run the above command, I get the 404 listed above. I asked certbot to stop prior to sending the challenge, and when I manually run wget http://lingnu.com/.well-known/acme-challenge/jSVVTObWuHMwqm2RtiGvcAQXos6liDfnOf_QvQx7p5s, I get the expected result and the site’s access log shows my access as 200.
I then press Enter, and get the response listed above (that the CA got a 404), but my access log does not show anyone accessing the site.
Since my laptop is IPv4 only, and the CA uses IPv6, I tried using a web tool that checks IPv6 access. It says the site is reachable, and my access log shows its connection.
This is not a transient problem. It affects all of my domains, and has been going on long enough for my certificates to begin nearing expiration.
I suspect I may have assigned them to an IP that belongs to the registrar. I’ll investigate when I have time.