The current definition of Instance in the RSSAC026 lexicon is somewhat ambiguous.
When anycast routing is used to allow more than one server to have the same IP address, each one of those servers is commonly referred to as an instance. For root servers, one refers to "an instance of J-root" to mean one of the network locations answering to J-root’s IP address.
The first sentence says it's a server, and the second sentence says it's a location. In the current draft, the definition has been changed to this:
*When anycast routing is used to allow more than one server to have the same IP address, each one of those servers is commonly referred to as an instance or anycast instance. For root servers, one refers to "an instance of J-root" to mean one of the network servers answering to one of J-root’s IP addresses.*
So now it's a server on one address (which implies there's another instance on J-root's other IP address). Paul thought this could use some discussion and I agree. In my mind, using the word 'server' to define something in this context is confusing. Is a server a piece of equipment or a software process? I think of an instance as "equipment used at a location used by an operator to provide DNS service". If I had to define it as a single word, I would say it's a location. At one location for D-root we have 4 Dell servers in the same rack. They are each talking BGP with a router that's using ECMP to reach them. Each Dell is answering on v4 and v6. I consider this one instance. What do others think? That's my $.02, -Karl