Как работают ssl сертификаты letsencript?

certbot renew --dry-run
Saving debug log to /var/log/letsencrypt/letsencrypt.log

-------------------------------------------------------------------------------
Processing /etc/letsencrypt/renewal/************.conf
-------------------------------------------------------------------------------
Cert is due for renewal, auto-renewing...
Starting new HTTPS connection (1): acme-staging.api.letsencrypt.org
Renewing an existing certificate
Performing the following challenges:
http-01 challenge for ************
Waiting for verification...
Cleaning up challenges
Generating key (2048 bits): /etc/letsencrypt/keys/0002_key-certbot.pem
Creating CSR: /etc/letsencrypt/csr/0002_csr-certbot.pem
** DRY RUN: simulating 'certbot renew' close to cert expiry
**          (The test certificates below have not been saved.)

Congratulations, all renewals succeeded. The following certs have been renewed:
  /etc/letsencrypt/live/**********/fullchain.pem (success)
** DRY RUN: simulating 'certbot renew' close to cert expiry
**          (The test certificates above have not been saved.)