[OpenAFS-devel] Re: AFSDB record changes and pre-existing clients

[Jeffrey E Altman]

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I'm moving this discussion to openafs-info@openafs.org because its
subject isn't about new or on-going development of OpenAFS.

OpenAFS 1.6 and later clients support both DNS AFSDB and SRV records.
AFSDB records have been deprecated by the IETF and are often unsupported
by SOHO routers that implement DNS proxies. DNS SRV records are widely
supported and should be used. There is no harm in publishing both types
but the clients will search for SRV records first.

OpenAFS clients will obtain the DNS response TTL and will use it to
expire the list of cell vlservers provided that the list was obtained
from DNS.  If the list is obtained from a CellServDB or from use of "fs
newcell" the cell's vlserver list will never expire.

Note that for OpenAFS the contents of the client's CellServDB file takes
precedence over DNS.  As long as there is a umich.edu entry in the
CellServDB the DNS records will be ignored.

OpenAFS currently ships with the following obtained from grand.central.or=
g:

  >umich.edu              #University of Michigan - Campus
  141.211.1.32                    #fear.ifs.umich.edu
  141.211.1.33                    #surprise.ifs.umich.edu
  141.211.1.34                    #ruthless.ifs.umich.edu

A further note.  The OpenAFS Unix cache managers use the IP addresses as
specified in the CellServDB file.  They ignore the hostnames which for
OpenAFS were only ever used by the Windows client.

The AuriStorFS client behavior is quite different. The cell vlserver
configuration that ships for umich.edu is secondary to DNS.  It is only
used when DNS SRV and DNS AFSDB queries fail.  AuriStor decided that we
never wanted to ship configuration information that would restrict a
cell's administrator from re-deploying the cell's infrastructure when
necessary.

Good luck.

Jeffrey Altman

On 7/19/2019 9:39 AM, Steve Simmons wrote:
> We're working a project to migrate our afsdb servers to a new data
> center in a manner that minimizes downtime for clients. As part of this=
,
> we're going to convert all the clients we control to use afsdb records
> in hopes of eliminating downtime completely. There are some edge
> conditions we didn't immediately see an answer for,=C2=A0 mostly relati=
ng to
> what a client does when the DNS AFSDB records change. We're looking at
> this w/r/t 1.6 and 1.8 clients. The questions we have -
>=20
> - does the client time out=C2=A0 the records in accordance with the TTL=
s and=C2=A0
> re-fetch them?
> - whether it does or not, is there=C2=A0 a way to force the client to r=
efetch
> without having to restart the client service or the entire client?
>=20
> Advance=C2=A0 thanks,
>=20
> Steve Simmons
> ITS Unix Support/SCS Admins

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fn:Jeffrey Altman
n:Altman;Jeffrey
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adr:;;255 W 94TH ST STE 6B;New York;NY;10025-6985;United States
email;internet:jaltman@auristor.com
title:CEO
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