On Apr 20, 2016, at 3:40 PM, cleaver at terabithia.org wrote:

Date: Wed, 20 Apr 2016 15:40:14 -0700 From: "J.C. Cleaver" <cleaver at terabithia.org> To: "Xymon Mailing List" <xymon at xymon.com> Subject: Re: [Xymon] Xymon disruption every night! Message-ID: <ffe8d4b5d0aa3d63517f2d994cf03d5c.squirrel at mail.kkytbs.net> Content-Type: text/plain;charset=iso-8859-1

On Wed, April 20, 2016 12:55 pm, Greg Earle wrote:

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On Feb 17, 2016, at 12:50 AM,"J.C. Cleaver" <cleaver at terabithia.org> wrote:

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• Why I have a "DNS error" here ? I set up the IP yesterday to this host to solve the issue. The "conn" error disappeared since yesterday evening but the http error still remains.

All signs do point to an issue with DNS resolution here.

Was this a custom compile or are you using a package? If custom, what version of c-ares is on your system? That's the underlying resolution library that xymonnet is using by default to handle DNS lookups. The fact that the 'conn' test remained good after you added the local hosts entry matches that, since HTTP tests are performed using their own secondary DNS lookup (to deal with vhosts, etc.) unless the IP is specified there as well.

J.C.,

I just stumbled across this thread from 2 months ago. We're having DNS glitches at my work and it's causing a flood of <hostname>:http "DNS error" alerts in Xymon, which is becoming a real problem.

But here's what I don't understand. All of our HTTP-tested hosts are in the "hosts.cfg" file with their short names (instead of FQHNs). So I couldn't understand why DNS was involved since the IP addresses and names were right there in "hosts.cfg" for Xymon to use.

Your response - specifically "unless the IP is specified there as well" - implies that there might be another location where I could load the names and addresses of our HTTP-tested hosts, to avoid this problem.

(Yes, I know - hosts and IP addresses can change. But I'm in control of that so I can deal.)

If this is the case, where is that other location where I can specify the short names/IP addresses for the HTTP tests?

Yep: https://xymon.com/help/manpages/man5/hosts.cfg.5.html#lbAR

192.168.0.10 mywebserver # http://www.sample.com=192.168.0.10/

For HTTP tests, an IP override is put in for each URL you're using. This will prevent a DNS lookup at http-test time for this URL, and when combined with combined with testip (for any other TCP checks here) and noconn (for ping->fping resolution), it should prevent any DNS lookups from being done for the string "mywebserver".

Unless there's been a regression, that should be sufficient. It's definitely worked at scale for mass testing of "hosts" that are not being referred to by a valid DNS name and simply listen on a distinct port.

Thank you!!! I had tried using "testip" in each of the Web server entries and couldn't understand why we still kept getting DNS meltdowns.

Apparently I missed this subtle line in hosts.cfg(5):

-- xymonnet ignores the "testip" tag normally used to force a test to use the IP-address from the hosts.cfg file instead of the hostname, when it performs http and https tests.

D'oh!

- Greg