Need help with a DNS config for a cluster

[Kevin Darcy]

Even without all of the expensive Coyote Point gear, you can configure your BIND
servers to give out multiple IP's in a "fixed" order (using the "rrset-order"
option available in later versions of BIND 8), but as Jim pointed out, there's
no guarantee that the clients will know how to do address failover. Also,
nameservers not under your control may interfere with your best-laid plans --
either Coyote Point's dynamic or BIND's native "fixed" rrset-order -- by giving
out the addresses with randomness or "cyclic"ness when answering from their
caches. So this falls far short of an optimal failover solution. My guess is
that Coyote Point resorts to the despicable TTL=0 practice in order to defeat
this caching effect. As if we need yet another product wasting bandwidth and
nameserver resources...


- Kevin

Spam Eater wrote:

> A white paper from Coyote Point claims that DNS can be configured to return
> multipl IPs (which it can), but they also say it can be configured in such a
> way that the client will try a second IP if the first one returned is not
> available.  I can't figure out how to do that. The best I can do is get my
> DNS to do round-robin which doesn't do any good if one of the returned
> addresses is unreachable.  How can I get it so the client tries all
> configured IPs?
>
> Below is their claim and they offer no example config.  The entire URL for
> those interested is: http://www.coyotepoint.com/cpenvoywp.pdf
>
> Thanks,
>
> Craig
>
> When a client browser addresses an HTTP request to
> http://www.coyotepoint.com, this fully-qualified
> domain name is resolved using Internet standard Domain Name Server (DNS)
> protocol. A "lookup" query
> is sent by the client to its local ISP or enterprise DNS [figure 1, step 1].
> The local DNS forwards the query
> to the "authoritative" DNS: in this case, the one responsible for
> coyotepoint.com [step 2]. The authoritative
> DNS returns IP addresses for the three Equalizers running Envoy. The client
> sends its HTTP request to the
> first IP address, trying other addresses if no response is received [step
> 3]. In this manner, the client's HTTP
> request is received by the first reachable Envoy site: in our example, New
> York.
>
> Each geographically-distributed, high-availability cluster is configured in
> three easy steps.
> 1. DNS Configuration: For each geographic cluster to be balanced, the
> authoritative name server must be
> configured to return name server and alias records for Envoys at every
> regional site. In our example,
> the authoritative DNS for coyotepoint.com delegates authority for
> www.coyotepoint.com to east, west,
> and europe.coyotepoint.com. When any client looks up www.coyotepoint.com,
> the queried delegate
> identifies all three Envoys in its DNS response.