[RSSAC Caucus] RSSAC026v2 definition of Instance

[Brian Dickson]

On Thu, Jan 23, 2020 at 12:18 PM Paul Vixie <paul at redbarn.org> wrote:

> On Thursday, 23 January 2020 18:59:19 UTC Karl Reuss wrote:
> > 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.
>
> i agree also.
>
> > 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.
>
> since we've known here of cases where two instances in adjacent racks each
> had
> multiple servers and its own local load balancer but spoke to two
> different
> internet exchanges which were present in the same data center, "location"
> is
> wrong. that's in fact where we got "instance".
>
> > 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?
>
> i agree, that's an "instance", because it is a dedicated collection of
> server
> and network equipment operated as a root name server, having upstream
> connectivity not shared by any other instance. however, a lot of rootops
> no
> longer operate their own equipment in some "location(s)", and so share
> server
> and network equipment with "instances" of other root servers. so,
> "instance"
> will have to be defined to account for virtualization including both the
> cloudflare model and the PCH model. i don't know yet exactly how to do
> that.
>
> noting that c-root has always used dedicated server equipment but has
> never
> had dedicated network equipment (it plugs into cogentco edge routers which
> may
> also serve other customers), "instance" may have to be defined in terms of
> unique servers which might be virtual, having unique upstream connectivity
> among other instances of the same root server. by leaving out "equipment"
> and
> leaving out "network", a version of "instance" might suit all current and
> contemplated root server deployments, including the cloudflare and PCH
> models.
>

I think it may be a bit cleaner to discuss anycast (generally) and then
what is meant by an anycast instance, and finally what an anycast instance
of a particular root server identity is.

Here's a brief attempt at this:

Anycast is the routing technique of advertising the reachability of a
> prefix from more than one router, typically (but not exclusively) as a
> global BGP announcement.

 An *anycast routing instance* is a single such routing announcement.

 The *anycast instance of a root server identity* is the server or set of
> servers reachable via a *single anycast routing instance* of the
> corresponding identity's IPv4 and/or IPv6 prefix.


It leaves unspecified any of the (IMHO unimportant details) of what the
servers actually are (physical/virtual, dedicated/shared), and leaves the
"network location" as an abstracted "anycast routing instance", for similar
reasons.
It also allows for flexibility in whether the servers are single-stack or
dual-stack for IPv4/IPv6 announcements/services.

Brian
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