My domain is:
mycloud.remysilber.com
I tried this ans work well 
root@reverse-proxy:/etc/nginx/sites-available# certbot certonly --force-renewal -a webroot -w /var/www/certbot_validation/ -d mycloud.remysilber.com
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Renewing an existing certificate
Performing the following challenges:
http-01 challenge for mycloud.remysilber.com
Using the webroot path /var/www/certbot_validation for all unmatched domains.
Waiting for verification…
Cleaning up challenges
Generating key (2048 bits): /etc/letsencrypt/keys/0017_key-certbot.pem
Creating CSR: /etc/letsencrypt/csr/0017_csr-certbot.pem
IMPORTANT NOTES:
-
Congratulations! Your certificate and chain have been saved at
/etc/letsencrypt/live/mycloud.remysilber.com/fullchain.pem. Your
cert will expire on 2018-01-02. To obtain a new or tweaked version
of this certificate in the future, simply run certbot again. To
non-interactively renew all of your certificates, run “certbot
renew” -
If you like Certbot, please consider supporting our work by:
Donating to ISRG / Let’s Encrypt: https://letsencrypt.org/donate
Donating to EFF: https://eff.org/donate-le
But when i run the rewew test it’s failled and i didn’t understand why.
Nothing clear in the log file /var/log/lestencrypt/letencrupt.log
root@reverse-proxy:/etc/nginx/sites-available# certbot renew --dry-runSaving debug log to /var/log/letsencrypt/letsencrypt.log
Processing /etc/letsencrypt/renewal/mycloud.remysilber.com.conf
Cert not due for renewal, but simulating renewal for dry run
Renewing an existing certificate
Performing the following challenges:
http-01 challenge for mycloud.remysilber.com
Waiting for verification…
Cleaning up challenges
Generating key (2048 bits): /etc/letsencrypt/keys/0018_key-certbot.pem
Creating CSR: /etc/letsencrypt/csr/0018_csr-certbot.pem
Attempting to renew cert from /etc/letsencrypt/renewal/mycloud.remysilber.com.conf produced an unexpected error: urn:acme:error:caa :: Error creating new cert :: Rechecking CAA: Internal error getting validation method for mycloud.remysilber.com. Skipping.
** DRY RUN: simulating ‘certbot renew’ close to cert expiry
** (The test certificates below have not been saved.)
All renewal attempts failed. The following certs could not be renewed:
/etc/letsencrypt/live/mycloud.remysilber.com/fullchain.pem (failure)
** DRY RUN: simulating ‘certbot renew’ close to cert expiry
** (The test certificates above have not been saved.)
1 renew failure(s), 0 parse failure(s)
Thanks for helping