Set up a pair of Ubuntu 18.04 servers following this guide: https://www.howtoforge.com/tutorial...ase-cluster-on-debian-8.4-with-ispconfig-3/5/ about 7 months ago. All I had to do in addition to that link was create a cron job to sync /etc/letsencrypt. Has been working fine since then, until last week when it was brought to my attention that the slave server wasn't serving any pages for one of the sites. MySQL is synced fine, site files and SSL certs are synced fine. Logged in to ISPconfig web interface on master and slave, compared settings for this site and they are identical on both. When I tested the site via the slave server, I got a cert error and so I compared the .vhost file on each server. They had similar timestamps but master server copy of the .vhost file has SSL* entries in it, slave doesn't, so when accessing the site via that server I get an SSL error because it's just serving the default cert not the site's proper cert. I turned up debugging on the slave server, made a trivial change to the site settings [ticked 'Perl'] in ISPconfig on the master server, waited a minute and I could see in /var/log/ispconfig/cron.log that it re-wrote the .vhost file on the slave: Code: 30.07.2019-16:05 - DEBUG - Calling function 'ssl' from plugin 'apache2_plugin' raised by event 'web_domain_update'. 30.07.2019-16:05 - DEBUG - Calling function 'update' from plugin 'apache2_plugin' raised by event 'web_domain_update'. 30.07.2019-16:05 - DEBUG - Add server alias: customer-domain.com 30.07.2019-16:05 - DEBUG - Creating fastcgi starter script: /var/www/php-fcgi-scripts/web12/.php-fcgi-starter 30.07.2019-16:05 - DEBUG - Enable SSL for: customer-domain.co.uk 30.07.2019-16:05 - DEBUG - Writing the vhost file: /etc/apache2/sites-available/customer-domain.co.uk.vhost 30.07.2019-16:05 - DEBUG - Apache status is: running 30.07.2019-16:05 - DEBUG - Calling function 'restartHttpd' from module 'web_module'. 30.07.2019-16:05 - DEBUG - Restarting httpd: systemctl restart apache2.service 30.07.2019-16:05 - DEBUG - Apache restart return value is: 0 30.07.2019-16:05 - DEBUG - Apache online status after restart is: running 30.07.2019-16:05 - DEBUG - Processed datalog_id 753 30.07.2019-16:05 - DEBUG - Remove Lock: /usr/local/ispconfig/server/temp/.ispconfig_lock finished. boom, site is working on slave server now. vhost file is identical on master and slave. ISPconfig version is 3.1.13. So, how can I prevent this happening in the future? Is it worth syncing these files with rsync?