Hi all, Well I've setup (4 years ago) a configuration similar to this one : https://www.howtoforge.com/tutorial...abase-cluster-on-debian-8.4-with-ispconfig-3/ (except that I was using unison instead of Dovecot to sync emails) Databases, emails and sites were all well synched on server2. server1 turned out to be offline. Bad thing is that all DNS zones were assigned to server1 in ISPConfig (on server2), ie : Client Server Zone NS Email client1 server1.domain.tld zone1.tld ns1.zone1.tld. [email protected] client2 server1.domain.tld zone2.tld ns1.zone2.tld. [email protected] So I was able to change the DNS values, but they were assigned to server1 (offline). There is no DNS inputs for server2.domain.tld Is that a normal case ? I had to manually edit every bind zone file to make DNS working (and stopping ISPConfig cronjob that would revert changes) Thanks a lot for your time.