# certbot certonly -a certbot-dns-aliyun:dns-aliyun --certbot-dns-aliyun:dns-aliyun-credentials /etc/letsencrypt/dns-aliyun-credentials.ini -d harboar.example.com
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator certbot-dns-aliyun:dns-aliyun, Installer None
Obtaining a new certificate
Performing the following challenges:
dns-01 challenge for harboar.example.com
Waiting 30 seconds for DNS changes to propagate
Waiting for verification...
Challenge failed for domain harboar.example.com
dns-01 challenge for harboar.example.com
Cleaning up challenges
Some challenges have failed.

IMPORTANT NOTES:
 - The following errors were reported by the server:

   Domain: harboar.example.com
   Type:   dns
   Detail: DNS problem: SERVFAIL looking up CAA for
   harboar.example.com - the domain's nameservers may be
   malfunctioning