title: How to create a Let’s Encrypt self signed certificate for a subdomain only? (error in post)
body: <p>How to create a Let’s Encrypt self signed certificate for a subdomain?</p>
  
  <p>To be specific:</p>
  
  <ul>
  <li><code>sub.domain.com</code> (needs a certificate and points to an ip address)</li>
  <li><code>domain.com</code> (does not point to anything)</li>
  </ul>
  
  <p>When following <a href="https://www.linode.com/docs/security/ssl/install-lets-encrypt-to-create-ssl-certificates" rel="nofollow noreferrer">the following instructions</a>, I get the following errors:</p>
  
  <pre><code>&gt;&gt;&gt; sudo -H ./letsencrypt-auto certonly --standalone -d sub.domain.com --register-unsafely-without-email
  Saving debug log to /var/log/letsencrypt/letsencrypt.log
  Plugins selected: Authenticator standalone, Installer None
  Obtaining a new certificate
  Performing the following challenges:
  tls-sni-01 challenge for sub.domain.com
  Waiting for verification...
  Cleaning up challenges
  Failed authorization procedure. sub.domain.com (tls-sni-01): urn:acme:error:connection :: The server could not connect to the client to verify the domain :: Timeout
  
  IMPORTANT NOTES:
   - The following errors were reported by the server:
  
     Domain: sub.domain.com
     Type:   connection
     Detail: Timeout
  
     To fix these errors, please make sure that your domain name was
     entered correctly and the DNS A/AAAA record(s) for that domain
     contain(s) the right IP address. Additionally, please check that
     your computer has a publicly routable IP address and that no
     firewalls are preventing the server from communicating with the
     client. If you're using the webroot plugin, you should also verify
     that you are serving files from the webroot path you provided.
  </code></pre>