Had a little problem with letsencrypt, when I tried to renew the certificates, the following error showed:

root@tsunade / # letsencrypt --renew-by-default
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Certbot doesn't know how to automatically configure the web server on this system. However, it can still get a certificate for you. Please run "certbot certonly" to do so. You'll need to manually configure your web server to use the resulting certificate.

So I looked in /var/log/letsencrypt/letsencrypt.log :

2017-08-20 18:43:37,178:DEBUG:certbot.main:Root logging level set at 20
2017-08-20 18:43:37,179:INFO:certbot.main:Saving debug log to /var/log/letsencrypt/letsencrypt.log
2017-08-20 18:43:37,179:DEBUG:certbot.main:certbot version: 0.10.2
2017-08-20 18:43:37,179:DEBUG:certbot.main:Arguments: ['--apache']
2017-08-20 18:43:37,180:DEBUG:certbot.main:Discovered plugins: PluginsRegistry(PluginEntryPoint#webroot,PluginEntryPoint#null,PluginEntryPoint#manual,PluginEntryPoint#standalone)
2017-08-20 18:43:37,180:DEBUG:certbot.plugins.selection:Requested authenticator apache and installer apache
2017-08-20 18:43:37,180:DEBUG:certbot.plugins.selection:No candidate plugin
2017-08-20 18:43:37,180:DEBUG:certbot.plugins.selection:Selected authenticator None and installer None

So…. I had no clue, but a quick search on stackoverflow showed that I missed a package

root@tsunade / # apt-get install python-certbot-apache
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  augeas-lenses libaugeas0 python-augeas

And all ended well. I renewed the certificates:

root@tsunade / # letsencrypt --renew-by-default
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Which names would you like to activate HTTPS for?
1: my domains
Select the appropriate numbers separated by commas and/or spaces, or leave input blank to select all options shown (Enter 'c' to cancel):
Starting new HTTPS connection (1): acme-v01.api.letsencrypt.org 
Renewing an existing certificate