[wxqc] cwop.aprs.net

[tim.mcmanus at mac.com]

The problem is easily solved if I can use your DNS servers and set it  
up so that when a server is dead, DNS drops it from the round robin  
list.

Perhaps a Nagios monitor that triggers an event that stops BIND,  
updates the DNS record and restarts BIND.  I'm not a programmer, but  
it seems simple enough (doesn't everything).

In understand it's a problem with Davis's software, but I'm not going  
to hold my breath for an update.

Thanks for the comprehensive update!

--
Tim McManus
tim.mcmanus at mac.com

> Date: Mon, 02 Jun 2008 12:39:42 -0400
> From: Ted Lum <gladstonefamily.net at tedworld.com>
> Subject: Re: [wxqc] cwop.aprs.net
> To: Discussion of weather data quality issues
> 	<wxqc at lists.gladstonefamily.net>
> Message-ID: <4844224E.7080204 at tedworld.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Linux/Unix will send back an ICMP "connection refused" in response  
> to an
> attempt to connect to a port where _nothing is listening_. This  
> differs
> slightly from Windows that just won't send ICMP so you end up  
> getting a
> socket timeout. Connection refused on a box is characteristic of a  
> dead
> process. Routers on the other hand return ICMP "destination  
> unreachable"
> because they can't route a packet, usually either due to route table
> errors or a route that has gone down. Servers do not send ICMP
> destination unreachable, only routers.
>
> Regardless, WeatherLink was architected poorly and would not try any
> other server no matter what comes back, and in some cases the
> application hangs and you have to restart it. This is the response I  
> got
> back from Davis on this topic:
>
> "I forwarded your email to our WeatherLink server person. He said  
> you are
> entirely right.  CWOP lists several servers and Weatherlink.com does  
> only try
> to upload to the first one.  He said he thought it would be a good  
> idea to
> try the others but haven't coded it yet.  He is aware of the problem  
> and it
> has been added to the our bug list. Thank you for the input."
>
> Davis are the only ones that can fix WeatherLink. There is no simple
> work around for this. The best that could be hopped for would be a
> solution that dynamically updates DNS when a server goes down. But due
> the how DNS works and how the internet is put together with DNS  
> caching
> all over the place, and not necessarily playing by all the same rules,
> it probably would still not be 100% effective. The server likely would
> be back up before all the stale records got aged out.
>
> Basically it goes like this. If the internet circuit goes down the
> gateway router will probably return "destination unreachable". There  
> are
> a whole lot of reasons you might get "destination unreachable" but  
> with
> the internet circuit usually being the most brittle that's the most
> likely cause. If the circuit is up and the path is good through the  
> last
> router, down to the subnet, but the server operating system or network
> stack is down (or your talking to a Windows box or there is a firewall
> in the way) you'll get a local socket timeout because nothing at all
> came back and your client got tired of waiting. If the O/S and network
> are up but the process that services requests on the port is either  
> not
> started or dead, you'll get "connection refused" (unless its Windows  
> or
> there is a firewall in the way) - "connection refused" = "no one is
> listening". These messages are implemented deep in the internet  
> protocol
> (ICMP and IP), they are not arbitrary messages that applications  
> create
> or send. Its the responsibility of the client application to  
> understand
> how the internet protocols work and do the right thing.
>
> -Ted-




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