rdnsd - a remote DNS server monitoring tool
rdnsd is a tool which can be used to monitor the availability and responsiveness remote DNS servers. Given a list of DNS servers, it will periodically query each server in turn and record whether a response was received, and how quickly. This information can then be obtained by sending a signal to the rdnsd process - a Munin plugin is provided as an example of how this can be achieved.
rdnsd [OPTIONS]
-
--help
Display help text.
-
--config=FILE
Specify the configuration file. See "CONFIGURATION FILE" for further details. Arguments passed on the command line will override the contents of this file.
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--debug
Enable debug mode.
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--loop=LOOP
Set loop duration.
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--pidfile=FILE
Specify pid file.
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--proto=QUESTION
Specify protocol.
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--question=QUESTION
Specify question.
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--timeout=TIMEOUT
Specify timeout.
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--recurse
Enable recursion.
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--servers=SERVERS
Specify servers to check.
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--statsfile=FILE
Specify stats file.
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--percentile=PERCENTILE
Specify a percentile to use when generating statistics.
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--domains=DOMAINS
Specify domain names to query for a list of servers.
The easiest way to configure rdnsd is to provide a configuration file. The format is very simple. Here is an example:
Debug false
PidFile /var/run/rdnsd.pid
StatsFile /var/run/rdnsd.log
Percentile 95
Protocol udp
Loop 3
Recurse false
Question . A IN
Servers ns1.example.com,ns2.example.net
Domains example.com
The directives are explained below. As noted above, if the equivalent command line argument is passed, it will override the value in the configuration file.
-
Debug (true|false)
Default: false
Normally, rdnsd will daemonise once started. If the
Debugparameter istrue, rdnsd will stay in the foreground and spam your terminal with debugging information. -
PidFile /path/to/pid/file
Default: var/run/rdnsd.pid
The file where rdnsd will write its pid.
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StatsFile /path/to/stats/file
Default: /var/run/rdnsd.log
The file where rdnsd will write statistics to when signalled. See "OBTAINING STATISTICS" for further information.
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Percentile PERCENTILE
If this option is set, rdnsd will calculate the response time at the given percentile. See "STATISTICS FILE FORMAT" for further information.
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Protocol (udp|tcp)
Default: udp
Specify the transport protocol to use.
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Loop SECONDS
Default: 2
This specifies the length of the main loop. If this is set to 2, then each server will be checked every 2 seconds. This value can be a decimal fraction, eg 0.25.
-
Recurse (true|false)
Default: false
Enable recursion.
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Question QUESTION
Default: example.com. IN A
Specify the DNS question. The format is "QNAME QCLASS QTYPE".
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Servers SERVERS
Default: none
Specify the servers to be checked. This directive can't be used at the same time as the "Domains" directive.
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Domains DOMAINS
Default: none
Rather than specifying a list of nameservers, you can provide a list of domains instead. For each domain, rdnsd will query for SRV records for _dns._udp under the domain and use the targets of any SRV records returned.
The SRV record is checked once at start-up, so if the list of hosts changes, you will need to restart rdnsd.
To get statistics out of rdnsd, send it the USR1 signal:
$ kill -USR1 `cat /path/to/pid/file`
This will cause rdnsd to dump its current data to the statistics file. If this file cannot be written to, rdnsd will terminate.
The statistics file will contain one line for each server that is being checked. Each line contains the nameserver checked, the response rate as a decimal fraction, and the average response time (in milliseconds), for example:
ns0.example.com 1.00 25
If the Percentile option is set in the config file (or the
--percentile argument was given), an additional value will appear at
the end of the line:
ns0.example.com 1.00 25 36
This value is the response time (in milliseconds) at the given percentile.
Once the file has been written, rdnsd's internal data is reset, so subsequent signals will produce fresh statistical data.
rdnsd is Copyright 2013 CentralNic Ltd. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.