BlueCat Crossover High Availability (xHA) provides disaster recovery through the use of redundant servers: xHA makes two DNS/DHCP Servers function as a single server. If one of the servers fails for any reason, the other takes its place and continues providing services.
The pair appears as a single server for DNS queries because both servers share an IP address. Each server in the pair has its own IP addresses for management through Address Manager.
Supported xHA pairs
| Hardware appliance 2 | Virtual machine 2 | |
|---|---|---|
| Hardware appliance 1 | xHA supported | xHA not supported |
| Virtual machine 1 | xHA not supported | xHA not supported* |
Supported xHA configurations
| Physical pair | Virtual pair | |
|---|---|---|
| xHA Backbone connection between pair (eth1) | Highly recommended | Highly recommended |
| Different software versions on each node | Not supported | Not supported |
| Different architecture on each node | Not supported | Not supported |
| w/ non-BlueCat failover enabled** | Not supported | Not supported |
Note: *Only supported where latency between the two virtual machines is roughly
equivalent to two physical appliances and where the two virtual machines aren't on the
same physical hypervisor host. If the latency between the virtual xHA pairs exceeds that
of two physical appliances, BlueCat recommends foregoing xHA in favor of the failover
capability provided by the hypervisor (if one exists), though we may not officially
test/support such features. **Such as VMware vMotion or Fault Tolerance.