GetBackend returns the specified backend ready for use or exits with a fatal error.

IPv4 means that the DNS records is a IPv4 address.

IPv6 means that the DNS records is a IPv4 address.

DummyBackend is a GoDDNS backend for debugging, it just prints the DNS record changes.

PowerDNSBackend is a GoDDNS backend for PowerDNS with PostgresSQL.

Backend is the interface for GoDDNS backend and allows a simple extension of GoDDNS.

AddressType is the address type of a DNS record: `IPv4` or `IPv6`.