A DNS zone is usually served by multiple authoritative servers, which is actually recommended for the sake of redundancy. Large authoritative DNS operators even combine different name server implementations to avoid complete infrastructure outage in case of any software error. For synchronizing zone contents between authoritative servers, a DNS-specific mechanism is available, called zone transfer. It is well established and supported by all common DNS implementations. It enables both full zone transfer (AXFR) and incremental update (IXFR).
Recently, version 3.0 of Knot DNS – an open-source implementation of an authoritative DNS server – has been released. Despite the version number, the software isn’t changing much. There are slightly more new features than in common feature releases such as 2.9. However, the features added in 3.0 don’t change any behaviour, unless the user turns them on. The migration from 2.9 to 3.0 is therefore seamless.