Dear Let's Encrypt Community,
I have encountered an interesting issue while testing Certificate Installation and renewal on a whitelisted domain (acme-challenge-test.domain_name.com) that allows traffic only from specific range of IP addresses. During this testing, I faced problem with the http-01 challenge failing with the following error.
Command used: certbot certonly --standalone -d acme-challenge-test.domain_name.com --http-01-port=8888 --debug-challenges -v
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Waiting for verification...
Challenge failed for domain acme-challenge-test.domain_name.com
http-01 challenge for acme-challenge-test.domain_name.com
Certbot failed to authenticate some domains (authenticator: standalone). The Certificate Authority reported these problems:
Detail: xxx.xxx.xxx.xxx: Fetching http://acme-challenge-test.domain_name.com/.well-known/acme-challenge/xUNTJyXuqVJM7CYhFWrWrrN4sKZPUqVfqlfadsfdfdsf: Error getting validation data
Hint: The Certificate Authority failed to download the challenge files from the temporary standalone webserver started by Certbot on port 8888. Ensure that the listed domains point to this machine and that it can accept inbound connections from the internet.
Cleaning up challenges
Some challenges have failed.
Ask for help or search for solutions at https://community.letsencrypt.org. See the logfile /var/log/letsencrypt/letsencrypt.log or re-run Certbot with -v for more details.
To resolve this issue, I decided to create the cert with DNS challenge, which completed successfully. Here's the command used for the same:
certbot -d acme-challenge-test.domain_name.com --manual --preferred-challenges dns certonly --debug-challenges -v
Interestingly, after the DNS challenge succeeded, I gave the http-01 challenge another shot and this time it worked without any issues (same command as above).
I am seeking your expertise to clarify on the following:
Question 1: Why did the http-01 challenge succeed on the second attempt? Could it be possible that the authentication was cached, and the second time it renewed the certificate without re-authentication?
Question 2: If caching is involved, where is this saved? And is there a way to clear the authentication cache to replicate the initial failure and investigate it further?
I have tried "resolvectl statistics" and "resolvectl flush-caches" to clear the cache (Ubuntu v22.04), but the behaviour persisted. I attempted to find any cache-related files in the certbot directories, but couldn't find anything apparently.
Question 3: What could be the reason behind the successful completion of the http-01 challenge after the DNS challenge? Is there a connection between these two challenges, especially considering that the http-01 challenge failed before the DNS challenge?
I would appreciate any insights or explanations that can help me better understand this behavior.
Thank you for your assistance!