USENIX 2004 Annual Technical Conference, FREENIX Track Abstract
Pp. 165168 of the Proceedings
A Software Approach to Distributing Requests for DNS Service Using GNU Zebra, ISC BIND 9, and FreeBSD
Joe Abley, Internet Systems Consortium, Inc.
This paper describes an approach for deploying authoritative
name servers using a cluster of hosts, across which the load of
client requests is distributed. DNS services deployed in this
fashion enjoy high availability and are also able to scale to
increasing request loads in a straightforward manner.
The approach described here does not employ any custom
load-balancing appliances (e.g. devices commonly marketed as
as "layer-four switches", "content switches" or "load-balancers");
instead the individual members of the cluster announce a service
address to one or more gateway routers by participating in routing
protocols to provide an intra-cluster anycast architecture.
Load-balancing appliances can sometimes present single points
of failure to a cluster. This problem is avoided using the
technique described in this paper; the only components required
to construct the cluster are the hosts that provide the service,
and one or more gateway routers which provide access to the rest
of the Internet.
The coupling between the DNS software and the routing software
needs to be sufficiently robust to ensure that a service address
is not advertised while requests cannot be satisfied. This
includes a description of a technique for announcing and
withdrawing the route for a service address such that availability
of the service in the routing system is coupled with the
ability to answer requests on individual hosts in the cluster.
The F Root Name Server is deployed using clusters built in this fashion, using FreeBSD, GNU Zebra and ISC BIND 9.
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