[Nagiosplug-devel] RFC: New threshold syntax

[William Leibzon]

> On Mon, Mar 17, 2008 at 2:15 PM, Ton Voon <ton.voon at altinity.com> wrote:
> Hi!
>
> I tried to get this through last year, but I don't think a conclusion
> was reached so I'm going to try again now!
>
> This is a proposal for a new threshold syntax. My motivation is that I
> have to update check_procs based on a customer's requested use for it.
> I'd like a generally applicable syntax, so that there is maximum code
> reuse and consistency.
>
> The proposal is here: http://nagiosplugins.org/rfc/new_threshold_syntax
>
> I've decided to use the website as this can be the master document. I
> plan on updating it based on people's comments. Hopefully it will not
> require too many alterations!
>
> Comments?

I'm going to comment on it even if its a bit late... And quickly my personal
"vote" would be NO, but I have mostly outsider perspective and NO does not
mean I'm like existing threshold either and have not used it when developing
my plugins until very recently. I probably will not participate in this
thread as I have only limited time right now but will answer specific
questions to me if there are any.

First of I'd like to note that above proposal moves to the idea that each
threshold is a separate parameter checked by plugin for which
critical/warning/ok are to be specified. For such a case the syntax could
work if the parameter to the plugin is stable and so can have its own
command line parameter. But this is not all so in every case. It is
especially not so for plugins that I write where parameters are called
attributes and are specified on command line to the plugin and their numbers
change depending on use. In such and similar cases it is a lot better to
have --warning and --critical command-line parameter and spec on how to
specify it. This is also what people are used to who used nagios for many
years. Additionally in new syntax you now have "ok", "warn", "crit" and that
I think would end up being confusing (and make code more difficult)
especially if people start specifying all 3 together. I also think that
people do not like it when you change plugin spec code too much/too often
and with nagios plugins you want to be as backward-compatible from one
release of the plugin to another (admins expect to be able to just drop in
your new version of code as replacement for what they currently have and
then they may look at use of new features and further changes). You maybe
able to support both as you'd specific new syntax as "crit=.." where as old
one did not have but supporting multiple syntax versions in same code makes
it larger and more difficult to maintain.

Now I'm not saying you should not do it and extend your current syntax if
there is a legitimate need and problems reported, just be warned about
consequences and difficulties... I also generally found you "range" based
syntax to be somewhat counter-intuitive and as far as a:b specifying alert
when OUTSIDE of the range. Perhaps this can be fixed fairly easily by
adapting new separator
(a..b is alert when >a and <b as proposed instead of @a:b) and having single
value (no 'a:b" just a) be understood as single upper threshold to be
compatible with how existing people have used nagios for years.

------

Now I'll give personal perspective of what I have done in my plugins and
custom spec I use (which I do not recommend you adapt but seeing it may help
in some way). In most of my plugins there are many "attributes" that are
checked as for example in:
 http://william.leibzon.org/nagios/plugins/check_mysqld.pl
where attributes are variables from "SHOW STATUS" and you specify which ones
to check (similar also for number of my other plugins at
http://william.leibzon.org/nagios such as check_snmp_temperature,
check_jboss and others; although code is older as far as thresholds parsing
in them but that will slowly get updated). So I adapted system where list of
Attributes are specified with one command line parameter (usually -a and
then alphanumeric list separated by ','), warning threshold values with
another (usually --warn with threshold spec values separated with ',' -
empty/no value if there is no threshold) and similarly critical. This turns
to work pretty well although you can argue that there are better ways to do
it... I also wrote code that handles threshold spec in my plugins (which is
largely same for every one) before I even knew there is "official threshold
spec". So doing it independently I created threshold syntax of [prefix]value
where prefix is one of "<",">",'=","!" specifying if alert (critical or
warning depending on where that is in) is to be issued when plugin data is
below, above or equal or not equal to value specified. Of the people I know
that use my plugins they find it all fairly straight forward but the symbols
are a bit of an issue because > and < are special symbols in bash, etc. so
result is often enough that for proper call to plugin you have to quote it
all in "" to work. At some point I came upon page about nagios plugins
threshold syntax (can't immediately remember url) and while I found that
syntax somewhat odd, when it came down to extending my syntax to support
ranges (which are really very really needed) I decided to use that to be
compatible with what others do and to support users who are familiar with
that spec. So currently this is a full spec documented in plugin code:

# Warning and critical thresholds are specified with '-w' and '-c' and each
# one must have exact same number of values to be checked (separated by ',')
# as number of variables specified with '-a'. Any values you dont want to
# compare you specify as ~ (or just not specify a value, i.e. ',,').
#
# There are also number of other one-letter modifiers that can be used
# as prefix before actual data value to direct how data is to be checked.
# These prefixes are as follows:
# > : issue alert if data is above this value (default for numeric value)
# < : issue alert if data is below this value (must be followed by number)
# = : issue alert if data is equal to this value (default for non-numeric)
# ! : issue alert if data is NOT equal to this value
#
# Additionally supported are two specifications of range formats:
# number1:number2 issue alert if data is OUTSIDE of range [number1..number2]
# i.e. alert if data<$number1 or data>$number2
# @number1:number2 issue alert if data is WITHIN range [number1..number2]
# i.e. alert if data>=$number and $data<=$number2

Well ok, going back to your new spec question and again taking personal
perspective, I can tell that if plugin syntax seriously changes, I probably
would not be willing to rewrite my code (although adding support for ".." to
work same as @a:b is easy enough and that I might do that) and I also have
no near-term plans to start using Nagios::Plugins library either (I think
its bloated and difficult but that is really issue for another discussion
which I do not want to start here).

William
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