* * * * *

         Navel-gazing on my unwillingness to learn a software package

It was a simple request at the Weekly Company Meeting: “Can we monitor the
number of SMTP (Simple Mail Transport Protocol) connections to our mail
servers, and have it graphed in Cacti [1]?” Breaking it down, the answer
appears to be yes, and I have no XXXXXXX clue.”

And that is bugging the XXXX out of me.

The first bit? Pretty easy actually.

By default, our servers are already tracking SMTP connections via iptables,
and it's a simple matter to pull the number out:

> iptables --list -vnx \
>       | grep 'state NEW tcp dpt:25' \
>       | awk '{print $1}'
>

Print the current state of iptables, pull out the line accepting incoming
connections to the SMTP port, and print the first column, which is the number
of packets (and thus, the number of connections).

Next up is to deliver this information via SNMP (Simple Network Management
Protocol). We're using net-snmp [2] and it indeed, does make it easy to
export information via SNMP. Take the above command, place it into a file
(thus making it a shell script). Then, in the SNMP configuration file:

> exec  .1.3.6.1.4.1.2021.9004 snmp_connection /root/bin/smpt_connection
>

Restart the SNMP server, and do your query:

> GenericUnixPrompt> snmpwalk XXXXXXXXXXXXXXXXXX .1.3.6.1.4.1.2021.9004
> UCD-SNMP-MIB::ucdavis.9004.1.1 = INTEGER: 1
> UCD-SNMP-MIB::ucdavis.9004.2.1 = STRING: "snmp_connection"
> UCD-SNMP-MIB::ucdavis.9004.3.1 = STRING: "/root/bin/snmp_connection"
> UCD-SNMP-MIB::ucdavis.9004.100.1 = INTEGER: 0
> UCD-SNMP-MIB::ucdavis.9004.101.1 = STRING: "62191"
> UCD-SNMP-MIB::ucdavis.9004.102.1 = INTEGER: 0
> UCD-SNMP-MIB::ucdavis.9004.103.1 = ""
> GenericUnixPrompt>
>

So okay, the value we want is a string, and not numeric, but at least we can
query it.

Now we get to Cacti.

Eight hours later and I've yet to get a graph out of Cacti.

I found a page that describes a similar setup [3], but check out section 3C
and the XML (eXtensible Markup Language) file that's created.

Now check out the SNMP Query XML Syntax [4] for Cacti.

I don't fault you for feeling confused. I'm a XXXXXXXXXX programmer who
writes CGI (Common Gateway Interface)s in C for fun [5], and I got horribly
confused.

I can't quite figure out how Cacti works. Oh sure, it's easy to install, and
monitoring devices isn't all that difficult (I find it rather randomly clunky
myself) but adding a new query to Cacti?

If there's a straightforward way of doing that, I haven't found it.

Somehow “Data Queries” are tied to the “Data Templates” although what that
connection is eludes me. It seems like you can specify a single SNMP query in
a “Data Template” but maybe not, because why have an XML file for the SNMP
query?

And the “Graph Templates” tie into this mess as well, although I'm still
puzzled at that one.

And the flow is weird—I'll be in the “Data Query” section, obstensibly making
a change to a “Data Query” and suddenly find myself in the “Data Template”
area after saving a change. Or sometimes in the “Graph Template” area.

Never the “Host Template” area though.

I'm finding it a horribly confusing process and it's bugging me that I can't
figure this out. I want to quit and say to Smirk, “Sorry, not possible,” and
that is bugging me, because I know it is possible, probably even with Cacti
if I just knew what to do.

I know what the problem is—my mental model of how this is supposed to work
doesn't match the mental model of the Cacti developers. And without that
clear mental model, the whole process under Cacti just doesn't make sense to
me.

I had the same problem with C when I first started using it. I had been
programming for years in Assembly, and there were certain cases where a
problem would have been trivial in Assembly but I was utterly lost for a
solution with C. Of course, over time, I gained the ability to “think” in C,
and now what was once problematic in C (but not in Assembly) is now trivial
in C.

But that took a few years though, and at least with C, the knowledge is still
useful. I'm doubting that the time I spend with Cacti will have the same
benefit over the long term.

And that's bugging me too, mainly because it seems like I'm justifying not
learning it at all.

[1] http://www.cacti.net/
[2] http://net-snmp.sourceforge.net/
[3] http://www.roth.lu/cacti-snmp-tut.htm
[4] http://www.cacti.net/downloads/docs/html/snmp_query_xml.html
[5] https://boston.conman.org/about/technical.html

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