[tdwg-tag] Recent DiGIR service disruption
vieglais at ku.edu
Wed Oct 8 08:06:38 CEST 2008
Apologies for cross posting.
Hopefully, most of you did not notice this, but if you did, here's
what happened. A problem with resolving the digir.net domain was
recently identified by John Wieczorek and possibly others. This
problem would have affected most, if not all DiGIR providers currently
operating. Once identified, the issue was promptly resolved, and
ongoing problems are unlikely.
This message provides further information about the problem, how it
was resolved, and how recurrence will be avoided to ensure continued
operation of the DiGIR infrastructure.
= Problem =
The DNS entry "digir.net" is an A record that must point to an IP
address. For several years digir.net resolved to the ip address of
"126.96.36.199" which is a Source Forge machine that is configured as
a VHOST for digir.net. At some point in the last 48hrs, 188.8.131.52
ceased to respond as a VHOST for digir.net. This meant that any web
service that was expecting to retrieve content from digir.net (e.g. http://digir.net/schema/protocol/2003/1.0/digir.xsd
) failed, with significant operational repercussions. For technical
reasons, most other digir.net DNS entries were unaffected (e.g. www.digir.net
= Resolution =
The new Source Forge VHOST servicing www.digir.net was identified as
"184.108.40.206", and the DNS entry for digir.net was updated
appropriately. Since the TTL on that DNS record was set relatively
short (600 seconds), the DNS infrastructure picked up the new
information fairly quickly, and testing indicates that digir.net URLs
are now being correctly resolved from several locations around the
= What You Need To Do =
Nothing. You should not notice any ongoing disruption.
= Ensuring Continued Operation =
There are three major issues that lead to this malfunction (#2 and #3
are informational only for developers of new services and tools):
1. We have no control over Source Forge, and nor should digir.net
infrastructure be dependent on them
2. Much of the existing installed DiGIR infrastructure references
"digir.net" directly and so DNS level indirection is not practical.
3. HTTP redirects need to be supported in service implementations
and their clients. I suspect that a lot of DiGIR software services
and clients do not follow redirects properly.
== Issue #1 ==
A DNS monitoring service is now in place that will update the DNS
entries if the source forge machine changes again.
Also, a replica of the DiGIR web material currently hosted by Source
Forge is being created on a machine that we have complete control over
and is located on a fast internet backbone. The replica machine will
be monitored with a system that will provide automatic notification to
appropriate contacts in the event of failure. This machine will be
located at the University of Kansas at least initially. Once
operational, the DNS entry for digir.net will be modified to point to
DNS services are handled by dyndns.org. Since their inception they
have provided a 100% uptime for their clients which includes domains
such as CNN, Mozilla, and Twitter. Since digir.net was an early
adopter of their services, the DNS service provided by DynDNS does not
expire. DNS registration does expire however, and this relatively
minor expense is covered by the University of Kansas with assistance
from the National Science Foundation.
== Issue #2 ==
In retrospect, something like "http://schema.digir.net" rather than "http://digir.net
" should have been used. This would have provided a low level (DNS)
mechanism for indirection that would have been unaffected by this
unanticipated hardware change. Altering these entries in DiGIR
providers and tools is really not practical at this stage, so it is
unlikely that this issue can be directly addressed.
== Issue #3 ==
HTTP offers a mechanism for temporary and permanent redirection. In
order to take advantage of this functionality, it is necessary for
HTTP clients to properly interpret the HTTP 301 and 307 status codes
and the respective response headers to determine the new location of
the resource being resolved. This is the mechanism employed by PURLs
and TinyURL for example. Unfortunately, many developers take short
cuts when building tools to retrieve content from URLs and avoid the
additional small amount of work necessary to handle redirect
messages. Where ever possible, developers of services and clients
should use libraries that at least properly handle HTTP redirects
which will allow the use of PURLs and other mechanisms for providing
an additional level of indirection in URL resolution where necessary.
Biodiversity Research Center
University of Kansas
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