DNS monitor project documentation tree

Program Design Document

User guide

DNSmon project overview

I want to write a DNS monitor program. This program will contain a lot of my thinking about how applications ought to be written. It will have:

A readonly configuration file, which will accept comments. It will contain:

An E-mail address to send messages to when things go wrong.
A default timeout value
An interval between checks
A list of hosts to look up, either as names or as dotted quads or both. For each host, there is an optional timeout value, and an optional list of nameservers to check. If the list of nameservers is blank, then DNSmon uses gethostbyname or gethostbyaddr to do the lookup, otherwise it uses the IP address or host name to do the lookup. If a nameserver is specified as a host name, then DNSmon uses gethostbyname to convert it an IP address
Command/status TCP port
Allowed IP addresses for command/status updates.

A readwrite state file which contains

A list of correct hostname/IP address lookups in the same format as /etc/hosts
A list of anomalies which are acceptable.
The last time the program ran successfully

A command line interface at startup which includes optoins for everything in the configuration file
A control/status port which uses TCP/IP

A command line contral/status interface, suitable for scripting
A status interface which uses VT100 graphics to display the state of the system
A browser interface
An X-windows interface

SNMP intrerface

Has anybody done anything like a DNS monitor before as an open source project?

I googoled "DNS monitor" and I found a page on SiteScope which can do the DNS monitoring, jabber alert and jabber monitor (an open source implementation of the jabber protocol), intermapper, there is a DNS monitoring tool available at SimpleDNS.com. So I don't find an open source DNS monitoring solution. Since sitescope can do DNS monitoring, Real Networks will probably use that. But I could still do it as an open source project and release it to the world.

Implementation of the DNS monitor: a road map

I assume that I am going to do the original version as a perl script. My road map is:

Version	Features
0.0	Configuration file, monitoring capability, send E-mail when something goes wrong
1.0	A command line interface at startup which includes options for everything in the configuration file plus a daemon flag and a debug flag
1.1	readwrite state file
1.2	Sense when the nameservers disagree about a host
1.3	Logging via the syslog facility
2.0	A control/status port which uses TCP/IP
2.1	A command line contral/status interface, suitable for scripting
2.2	A status interface which uses VT100 graphics to display the state of the system
2.2	A browser interface
2.3	An X-windows interface
3.0	SNMP intrerface
4.0	rewrite in C

Outline

parse arguments

real configuration file and build host list and  ns list

bind to command/status tcp port   # version 2.0

change EUID/EGID           
      

fork SNMP interface           
   # version 3.0

fork command/status handler       # version 2.0

foreach host in hostlist

   foreach ns in nslist[host]

     status = green

     set alarm

     start timer

     if host is dotted quad then

       ip_name = reverse_query (host, ns)

     else

       ip_addr = query ( host, ns )

     endif

     if alarm timeout then status = red

     if time exceeds threshold then status = orange

     if answer is wrong then status =
yellow   # version 1.2

     change state to reflect status  
         # version 1.1

     if status != green and state is green or

        status == green and state is not
green then log using syslog   # version 1.3

   done

done

The command/status port thread (version 2.0):

do forever listen on command/status port wait for connection fork a connection handler done

connection handler