Import New Threshold Syntax proposal

Many sites have links to our New Threshold Syntax proposal, so lets put
it back online.  However, as we decided not to implement the New
Threshold Syntax anytime soon, we currently don't add a link to the
proposal on our own web site.

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+title: New Threshold Syntax
+parent: Documentation
+---
+
+<!--% # Auto-imported from: http://nagiosplugins.org/rfc/new_threshold_syntax # %-->
+
+# New Specification Method for Thresholds
+
+_Ton Voon, March 17, 2008_
+
+## Overview
+
+The method for defining thresholds via the command line is inconsistent and
+difficult to interpret. This proposal suggests a different way of specifying
+thresholds, which will also changes the metrics of performance data returned.
+
+## Problem
+
+The current method of specifying thresholds is confusing when there are
+different checks required. For instance, in check\_http, to check page size
+and time, you can specify -w {warn time}, -c {crit time}, -m
+{minpagesize}[:maxpagesize], -M {maxage of document}.
+
+Also, note the ways of defining the range are inconsistent. Some alert above
+the value (time, maxage), some alert below the value (pagesize). This is
+inconsistent for the same plugin!
+
+So, to check that a web page is returned within 5 seconds, the minimum page
+size is 10K and the maximum age is 1 day, you would invoke:
+
+    check_http -H $HOSTADDRESS$ -c 5 -m 10000 -M 1d
+
+Furthermore, the current specification for ranges in the developer guidelines
+fails the “obviousness” test: a range of 3:5 will alert if the value is
+outside that range, rather than inside as you would expect.
+
+Also, the performance data returned by check\_http is always time and size.
+Perhaps you want only time, or you want age as well.
+
+## Proposal
+
+### Thresholds
+
+This document proposes that threshold arguments are specified like:
+
+    --threshold={threshold definition}
+    --th={threshold definition}
+
+The threshold definition is a subgetopt format of the form:
+
+    metric={metric},ok={range},warn={range},crit={range},unit={unit},prefix={SI prefix}
+
+Where:
+
+-   ok, warn, crit are called “levels”
+-   any of ok, warn, crit, unit or prefix are optional
+-   if ok, warning and critical are not specified, then no alert is raised,
+    but the performance data will be returned
+-   the unit can be specified with plugins that do not know about the type of
+    value returned (SNMP, Windows performance counters, etc.)
+-   the prefix is used to multiply the input range and possibly for display
+    data. The prefixes allowed are defined by NIST:  
+    <http://physics.nist.gov/cuu/Units/prefixes.html>  
+    <http://physics.nist.gov/cuu/Units/binary.html>
+-   ok, warning or critical can be repeated to define an additional range.
+    This allows non-continuous ranges to be defined
+-   warning can be abbreviated to warn or w
+-   critical can be abbreviated to crit or c
+
+### Simple Range
+
+The range values have two specifications: simple and complex. Simple ranges
+are of the format:
+
+    start..end
+
+Where:
+
+-   start and end must be defined
+-   start and end match the regular expression
+    /^[+-]?[0-9]+\\.?[0-9]\*$|^inf$/ (ie, a numeric or “inf”)
+-   start ≤ end
+-   if start = “inf”, this is negative infinity. This can also be written as
+    “-inf”
+-   if end = “inf”, this is positive infinity
+-   endpoints are inclusive of the range
+-   alert is raised if value is inside start and end range
+
+(Note: this may be extended in future for adding multiple ranges using a
+separator - I think this is catered for by repeating ok=,warn=,crit=.)
+
+This simple range does not require quoting at the shell.
+
+### Complex Range
+
+Complex ranges are defined as:
+
+    [^](start..end)
+
+or
+
+    [^]start..end
+
+Where:
+
+-   start and end must be defined
+-   start and end match the regular expression
+    /\^[+-]?[0-9]+\\.?[0-9]\*\$|\^inf\$/ (ie, a numeric or “inf”)
+-   start ≤ end
+-   if start = “inf”, this is negative infinity. This can also be written as
+    “-inf”
+-   if end = “inf”, this is positive infinity
+-   endpoints are excluded from the range if () are used, otherwise endpoints
+    are included in the range
+-   alert is raised if value is within start and end range, unless \^ is used,
+    in which case alert is raised if outside the range
+
+Note that due to shell characters, quoting may be required.
+
+### Rules for Determining State
+
+Given a numeric value, the state of the threshold is calculated from the
+following ordered rules:
+
+1.  If no levels are specified, return OK
+2.  If an ok level is specified and value is within range, return OK
+3.  If a critical level is specified and value is within range, return
+    CRITICAL
+4.  If a warning level is specified and value is within range, return WARNING
+5.  If an ok level is specified, return CRITICAL
+6.  Otherwise return OK
+
+### Looking Back …
+
+So the check\_http example becomes:
+
+    check_http -H $HOSTADDRESS$ \
+               --th metric=time,ok=0..5 \
+               --th metric=size,ok=10..inf,prefix=Ki \
+               --th metric=age,ok=0..1,unit=d
+
+I believe this is more readable (I’m interested in the time, the size and the
+age) and more consistent (I’m alerting above 5, less than 10 and above 1,
+respectively).
+
+In addition, performance data will only be output if the metric has been
+specified. So only show time performance data if “--th metric=time” has been
+specified on the command line. Both warning\_range or critical\_range can be
+unspecified - this effectively means “I am not going to alert on this value,
+but I’d like to be informed about it in the performance data”.
+
+Because the specification for a range has changed, the warning and critical
+parts of the performance data can no longer be guaranteed. There is an
+additional piece of work required to fix a new format for performance data.
+However, the basic
+
+    label=value[uom]
+
+Will still be valid.
+
+### Examples
+
+Other examples.
+
+To check httpd processes are OK if the virtual size is under 8096 bytes. Warn
+until they reach 16182, but bigger than that is CRITICAL.
+
+    # old
+    check_procs -w 8096 -c 16182 -C httpd --metric VSZ
+
+    # new
+    check_procs -C httpd --th metric=vsize,ok=0..8096,warn=8097..16182
+
+There should always be one and only one ‘tnslsnr’ process. Otherwise
+critical.
+
+    # old
+    check_procs -w 1:1 -c 1:1 -C tnslsnr
+
+    # new
+    check_procs -C tnslsnr --th metric=count,ok=1..1
+
+Load averages (1,5,15 minute) should be within reasonable ranges.
+
+    # old
+    check_load -w 1.0,0.8,0.7 -c 1.5,1.3,1.0
+
+    # new
+    check_load --th metric=1min,ok=0..1.0,warn=1.0..1.5 \
+               --th metric=5min,ok=0..0.8,warn=0.8..1.3 \
+               --th metric=15min,ok=0..0.7,warn=0.7..1.0
+
+## Plan
+
+I personally plan on updating check\_procs.
+
+The basic syntax is:
+
+    check_procs [filter options] [threshold options]
+
+Where filter options are the current -u {username}, -C {command}, etc. This
+reduces the set of processes that are to be calculated.
+
+The new threshold metrics will be:
+
+-   number - alert on number of matching processes. Performance data returns
+    number of processes
+-   rss-threshold - alert on rss size if any matching process is in range.
+    Perf data returns average rss
+-   rss-max - Same as --rss, but perf data returns max rss
+-   rss-sum - alert on the total rss of all matching processes. Perf data
+    returns rss\_sum
+-   vsz-threshold - alert on vsz size if any matching process is in range.
+    Perf data returns average vsz
+-   vsz-max - Same as --vsz, but perf data returns max rss
+-   vsz-sum - alert on the total vsz of all matching processes. Perf data
+    returns vsz\_sum
+-   cpu-threshold - alert on cpu % of all matching processes. Perf data
+    returns average cpu
+-   cpu-max - Same as --cpu, but perf data returns max cpu
+-   cpu-sum - alert on total cpu. Perf data returns cpu\_sum
+
+There will be C library routines for parsing the threshold values.
+
+There will be C library routines for the collection and output of the
+performance data.
+
+## Terminology
+
+**metric**
+:   Something that a check is going to be measured against. For example, for
+    disk checks, it could be used or free or inodes\_free; for http checks, it
+    could be time [taken] or size; for process checks, it could be cpu or
+    number [of processes] or vsz
+
+**range**
+:   This defines a continuous range of values when an alert would be raised
+
+**level**
+:   This is an alert level within Nagios - OK, WARNING or CRITICAL
+
+**threshold**
+:   This consists of a level with a range
+
+## Limitations
+
+This assumes that you are always comparing numbers as the metric values.
+
+There maybe some limitations in the precision of values. All internal logic
+should use double precision.
+
+If there are multiple metrics, the alert will be on an OR basis, that is, any
+single metric which passes its threshold will cause the plugin to return a
+failed state.
+
+<!--% # vim:set filetype=markdown textwidth=78 joinspaces: # %-->