Dan Brown wrote:
On Wed, 25 Oct 2006, Ray Wells wrote:
Gerry Creager wrote:
But do you *need* to connect to each of the servers? Connecting to
the Core at one point, and using a rotate scheme, should accomplish
what you would want, the ability to fail over another server when,
albeit rarely, we have a server die.
Multiple connections to multiple servers tends to lead to loops on the
servers. AE5PL's done a lot of work to stop that and the Core sysops
have periodically gone thru and individually asked folks to help us
stamp out redundant connections.
gerry
Hi Jerry,
No, I don't need to connect to each server at the same time. All I'm
looking for is a redundancy scheme whereby if one server falls over,
Xastir will attempt to connect to an alternative server in a manner
similar to UIView.
Server failures are rare but, in accordance with Murphy's Law they will
happen when I'm not here, which is quite often, and I want to cover that
possibility.
I believe that this has been somewhat implemented by the APRS IS guys using
round robin DNS records with a 60 second (or so) ttl for "rotate.aprs.net"
Using "dig" on a command line:
------------------------------------------------------
Myhost.foo$ dig rotate.aprs.net
; <<>> DiG 9.2.1 <<>> rotate.aprs.net
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6864
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 2, ADDITIONAL: 2
;; QUESTION SECTION:
;rotate.aprs.net. IN A
;; ANSWER SECTION:
rotate.aprs.net. 46 IN A 165.91.140.28
rotate.aprs.net. 46 IN A 64.58.200.20
rotate.aprs.net. 46 IN A 134.173.254.38
;; AUTHORITY SECTION:
aprs.net. 5986 IN NS ns3.aprs.net.
aprs.net. 5986 IN NS ns7.aprs.net.
;; ADDITIONAL SECTION:
ns3.aprs.net. 5986 IN A 24.123.66.139
ns7.aprs.net. 5986 IN A 64.58.207.2
;; Query time: 47 msec
;; SERVER: 192.168.1.7#53(192.168.1.7)
;; WHEN: Tue Oct 24 19:56:43 2006
;; MSG SIZE rcvd: 149
------------------------------------------------------
If you use dig a few times in a row, you'll see the 3 lines in the "Answer
section" change order, and the TTL (46 here) will decrease over time. I've
not looked at the Xastir code, but, As long as users use hostnames and
xastir (and other stuff like nscd) doesn't cache the Hostname->Ip mapping
any longer than specified, you should be able fail over by using
"rotate.aprs.net" within 60 seconds, plus or minus timeouts to see if things
are truely down.
Still, it would be nice functionality to have -- use one "interface"
specification and have multiple possible hostnames to connect to. I
personally just have multiple interface specifications. If one goes down,
I can start another manually, fairly easily.
I am new to xastir myself, and yes, UI-View and WinAPRS and others use
"one" server, which does all that if I understand what is being
attempted there..
Just set xastir up to connect to rotate.aprs2.net port 14580 and supply
a filter like m/50 for 50 km from your position. When one server that
you might be connected to drops out, within a few second you will be
connected to another one without any intervention by you.. Since a few
days ago only, I have used rotate.aprs2.net. Not long enough to tell
about dropping from a server. My UI-View station drops only when I get a
clitch in my router, or I kill the program for one reason or another.
That being said, did I miss something here? Were you discussing
something different... :-) Sorry if I didn't get it...
Robbie
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