[5pt] Fully-distributed DNS with redundancy

[ivan-cukic]

This is a follow-up of the basic DNS implementation #37

coarse implementation details of what needs to be done -- assuming that we have already an implementation for a single instance DNS:

• Load Balancing: user may send the request to servers in a round-robin fashion and/or 'DNS Anycast'-style
• Synchronisation between DNS instances - the DNS should subscribe to each other, notify/publish their local changes when entries are added or expire, and update accordingly if the last update time-stamp if newer than the own copy (N.B. need to find a solution how to detect/handle clock mismatches)
• optional: investigate whether the pub/sub could be replaced by IP multicast as this would minimise the required local setup/registering of DNS IP addresses.