The Monitoring Plugins Interface
draft-kaestle-monitoring-plugins-interface-04
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Lorenz Kästle | ||
| Last updated | 2024-03-22 | ||
| RFC stream | Independent Submission | ||
| Intended RFC status | Informational | ||
| Formats | |||
| Stream | ISE state | In ISE Review | |
| Consensus boilerplate | Unknown | ||
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draft-kaestle-monitoring-plugins-interface-04
Network Working Group L. Kästle
Internet-Draft The Monitoring Plugins Project
Intended status: Informational 22 March 2024
Expires: 23 September 2024
The Monitoring Plugins Interface
draft-kaestle-monitoring-plugins-interface-04
Abstract
This document aims to document the Monitoring Plugin Interface, a
standard more or less strictly implemented by different network
monitoring solutions. Implementers and Users of network monitoring
solutions, monitoring plugins and libraries can use this as a
reference point as to how these programs interface with each other.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-kaestle-monitoring-plugins-
interface/.
Source for this draft and an issue tracker can be found at
https://github.com/RincewindsHat/rfc-monitoring-plugins-interface.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 23 September 2024.
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Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Wording, Context and Scope . . . . . . . . . . . . . . . 4
1.1.1. Wording . . . . . . . . . . . . . . . . . . . . . . . 4
1.1.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 6
2.1. Range expressions . . . . . . . . . . . . . . . . . . . . 6
2.1.1. Examples . . . . . . . . . . . . . . . . . . . . . . 8
3. Input Parameters for a Monitoring Plugin . . . . . . . . . . 8
3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 12
4. Output of a Monitoring Plugin . . . . . . . . . . . . . . . . 14
4.1. Exit Code . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2. Textual Output . . . . . . . . . . . . . . . . . . . . . 16
4.2.1. Free form output . . . . . . . . . . . . . . . . . . 17
4.2.2. Performance data . . . . . . . . . . . . . . . . . . 18
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 19
6. Security Considerations . . . . . . . . . . . . . . . . . . . 19
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
8. Normative References . . . . . . . . . . . . . . . . . . . . 20
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
Maintaining computer networks and providing services to machines,
networks and humans is a complex task. Building infrastructures from
the start commonly demands huge know-how in different technologies,
but maintaining them afterwards is in many cases often more
demanding. Complex system can fail in a multitude of different way,
where the original problem might lead to symptoms which are often not
immediately obvious and likely occur in a different place relative to
the problem.
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To ensure continuous and reliable operation the state and the
functionality has to monitored permanently with appropriate tools.
These monitoring tools allow an operator, often a system and/or
network administrator to read the state of the whole system (or
specific subsystems) and detect problems when they occur.
The purpose of monitoring tools is therefore to determine the state
of the systems in question and detect possible anomalies or problems,
measuring performance related metrics, process that data, produce a
human tangible representation and take action according to certain
rules, notify a system administrator for example. A system
implementing most or all of those tasks is called a "monitoring
system" in the following.
With the emergence of NetSaint/Nagios at the latest, a group of
network monitoring systems have relied on a loose group of programs
called "Monitoring Plugins" to do the lower level task of actually
determining the state of a particular entity or conduct measurements
of certain values.
The same interface was implemented by several different monitoring
solutions, including, without claiming completeness, Icinga, Icinga2,
Shinken, Naemon, Centreon and Opsview.
On the other side of this interface there are hundreds of individual
plugins developed by different people in different languages for a
multitude of purposes.
Examples for these are:
* The monitoring plugins https://www.monitoring-plugins.org/
* The nagios plugins https://nagios-plugins.org/
* Several monitoring plugins by Consol https://labs.consol.de/de/
nagios/
* Several monitoring plugins by Linuxfabrik
https://github.com/Linuxfabrik/monitoring-plugins
* Several monitoring plugins by Davide Madrisan
https://github.com/Linuxfabrik/monitoring-plugins
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This document shall serve administrators of those monitoring systems
and especially developers of these monitoring plugins and monitoring
systems as a basis on how this interface should implemented, how the
plugins should work and how they should behave. It encourages the
standardization of libraries, monitoring plugins and monitoring
systems, to reduce the cognitive load on administrators and
developers, when they work with different implementations.
+--------------------+
| Visualisation tool +------------+
+--------------------+ |
|
+-----------------+ exec +-------------------+
| Monitoring tool +--------+ Monitoring Plugin |
+-----------------+ +-------------------+
+--------------------+ |
| Notification tool +------------+
+--------------------+
This document aims to be as general as possible and not to assume a
special implementation detail, e.g. the programming language, the
install mechanism or the monitoring system which executes the
monitoring plugin.
1.1. Wording, Context and Scope
1.1.1. Wording
1.1.1.1. Monitoring system
A _monitoring system_ is a collection of software components which
serve the purpose of providing the system administrator of a
particular system with an overview of the whole system. This ideally
includes all of the devices, machines and components and their state
as well as insights on particular components.
Most of the system mentioned here (for example Icinga, Naemon and
Nagios) also provide a functionality to send notifications to the
system administrator when something goes wrong, e.g. a particular
component does not respond anymore or a certain threshold is
exceeded.
For the purpose of this document a monitoring system is just "the
thing that executes a monitoring plugin".
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1.1.1.2. Monitoring plugin
A monitoring plugin is a standalone executable, which is executed by
the monitoring systems to conduct one or multiple tests on behalf of
the monitoring system.
The monitoring plugin does not rely on functionality provided by the
monitoring system and is not a builtin of the monitoring system or
linked against certain components of the monitoring system.
Therefore it can also be executed manually and independently of a
particular monitoring system.
The monitoring plugin can therefor be implemented independently of
the monitoring system, it does not share necessarily share
dependencies, the programming language or the distribution mechanism
or other components with the monitoring system.
The monitoring plugin MAY accept parameters in the form of command
line arguments, environment variables or configuration files (the
location of which MAY in turn be given on the command line or via
environment variable).
The monitoring plugin then proceeds to execute its duty and returns
the result to the Monitoring System. Part of the process of
returning the result is the termination of the execution of the
Monitoring Plugin itself.
The execution of a monitoring plugin is typically short lived (in the
order of seconds or milliseconds) and, while some implementations
store some state on non-volatile memory to be able to reason over
several execution cycles, this is not considered best practice. A
monitoring plugin can not depend on any information other that which
was given by the calling monitoring system, since the monitoring
system might execute the plugin from a different system in the next
cycle or switch between multiple systems.
A reasonable approach to thinking about monitoring plugins is to
picture a "snapshot" of a current state, each execution independent
from the others and wholly dependent on the input parameters and the
"thing" that is to be monitored.
This "thing" which is to be monitored is not, in principle,
restricted to any specific aspect of IT systems, apart from the
restrictions above and the general concept. Examples for areas which
are difficult to cover whith this approach, are statistical analyses
of time series data or event monitoring, such as log monitoring.
However querying system, which are collecting and processing this
kind of data, would be a valid indirection.
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A popular example for this behaviour is the extraction of bandwith
usage on most switches. Commonly this is only exposed as counters
for each network interface, one for outgoing and one for incoming
bytes. The absolute value of bytes is practically useless without
knowing the value which was read previously and the time difference
between the probes. In this scenario, different workaround are
possible, if the device itself does not provide the rate values:
* The monitoring plugin queries the values several times during its
execution cycle with a know time difference between the queries,
which allows rate calculation in this (typically) short time
frame. Nothing is know effectively about the time between
execution cycles.
* The monitoring system executes the monitoring plugin with the data
and date of the last execution as parameter, which allows for
proper rate calculation.
* A system queries the devices regularly for the absolute values and
stores them. The monitoring plugin then queries this system for
the collected values (and timestamps) or directly for a
statistical analysis
1.1.2. Scope
The scope of this document is limited to the interaction of a
monitoring system and a monitoring plugin, meaning the interface
connecting them.
It does not attempt to describe the inner workings of a specific
implementation of either monitoring system or monitoring plugin.
2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.1. Range expressions
In many cases thresholds for metrics mark a certain range of values
where the values are considered to be good or bad depending on
whether they are inside or outside of this range. For a significant
number of metrics an upper (e.g. load on unixoid systems) or lower
(e.g. effective throughput, free space in memory or storage) border
might suffice, for some it does not, for example a temperature value
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from a temperature sensor should be within certain range (e.g.
between 10℃ and 45℃).
Regarding input parameters this might be handled with options like --
critical-upper-temperature and --critical-lower-temperature, but this
creates a problem in the performance data output, if only scalar
values could be used. To resolve this situation the _Range
expression_ format was introduced, with the following definition:
range-expression = [direction-switch] bounds
bounds = (lower-bound / upper-bound) / lower-bound upper-bound
direction-switch = "@"
lower-bound = NUMERAL ":"
upper-bound = NUMERAL
NUMERAL = ["-"] 1*DIGIT [ "." 1*DIGIT ] ; numerical value, either integer or floating point
where:
1. At least start or end MUST be provided.
2. start <= end
3. If start == 0, then start can be omitted.
4. If end is omitted, it has the "value" of positive infinity.
5. Negative infinity can be specified with the tilde character ~.
6. If the prefix @ IS given, the value exceeds the threshold if it
is INSIDE the range between start and end (including the
endpoints).
7. If the prefix @ is NOT given, the value exceeds the threshold if
it is OUTSIDE of the range between start and end (including the
endpoints).
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2.1.1. Examples
+==================+===============================================+
| Range definition | Exceeds threshold if x... |
+==================+===============================================+
| 10 | < 0 or > 10, (outside the range of {0 .. 10}) |
+------------------+-----------------------------------------------+
| 10: | < 10, (outside {10 .. ∞}) |
+------------------+-----------------------------------------------+
| ~:10 | > 10, (outside the range of {-∞ .. 10}) |
+------------------+-----------------------------------------------+
| 10:20 | < 10 or > 20, (outside the range of {10 .. |
| | 20}) |
+------------------+-----------------------------------------------+
| @10:20 | ≥ 10 and ≤ 20, (inside the range of {10 .. |
| | 20}) |
+------------------+-----------------------------------------------+
Table 1
3. Input Parameters for a Monitoring Plugin
A Monitoring Plugin MUST expect input parameters as arguments during
execution, if any are needed/expected at all. It MAY accept these
parameters given as _environment variables_ and it MAY accept them in
a configuration file (with a default path or a path given via
arguments or _environment variables_).
In general positional arguments are strongly discouraged.
Some arguments MUST have this predetermined meaning, if they are
used:
+==========+=========+===============+=============+========+===========+
|Argument |Argument |Argument |Meaning |optional|can be |
|(long) |(short | | | |given |
| |version, | | | |multiple |
| |optional)| | | |times |
+==========+=========+===============+=============+========+===========+
|--help |-h |None |Triggers the |no |-- (makes |
| | | |help | |no |
| | | |functionality| |difference)|
| | | |of the | | |
| | | |Monitoring | | |
| | | |Plugin, | | |
| | | |showing the | | |
| | | |individual | | |
| | | |parameters | | |
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| | | |and their | | |
| | | |meaning, | | |
| | | |examples for | | |
| | | |usage of the | | |
| | | |Monitoring | | |
| | | |Plugin and | | |
| | | |general | | |
| | | |remarks about| | |
| | | |the how and | | |
| | | |why of the | | |
| | | |Monitoring | | |
| | | |Plugin. | | |
| | | |SHOULD | | |
| | | |overwrite all| | |
| | | |other | | |
| | | |options, | | |
| | | |meaning, they| | |
| | | |are ignored | | |
| | | |if --help is | | |
| | | |given. The | | |
| | | |Monitoring | | |
| | | |Plugin SHOULD| | |
| | | |exit with | | |
| | | |state UNKNOWN| | |
| | | |(3). | | |
+----------+---------+---------------+-------------+--------+-----------+
|--version |-V |None |Shows the |no |-- (makes |
| | | |version of | |no |
| | | |the | |difference)|
| | | |Monitoring | | |
| | | |Plugin to | | |
| | | |allow users | | |
| | | |to report | | |
| | | |errors better| | |
| | | |and therefore| | |
| | | |help them and| | |
| | | |the | | |
| | | |developers. | | |
| | | |The | | |
| | | |Monitoring | | |
| | | |Plugin SHOULD| | |
| | | |exit with | | |
| | | |state UNKNOWN| | |
| | | |(3). | | |
+----------+---------+---------------+-------------+--------+-----------+
|--timeout |-t |Integer |Sets a limit |no |no |
| | |(meaning |for the time | | |
| | |seconds) or a |which a | | |
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| | |time duration |Monitoring | | |
| | |string |Plugin is | | |
| | | |given to | | |
| | | |execute. | | |
| | | |This is there| | |
| | | |to enforce | | |
| | | |the abortion | | |
| | | |of the test | | |
| | | |and improve | | |
| | | |the reaction | | |
| | | |time of the | | |
| | | |Monitoring | | |
| | | |System (e.g. | | |
| | | |in bad | | |
| | | |network | | |
| | | |conditions it| | |
| | | |might be | | |
| | | |helpful to | | |
| | | |abort the | | |
| | | |test | | |
| | | |prematurely | | |
| | | |and inform | | |
| | | |the user | | |
| | | |about that, | | |
| | | |than trying | | |
| | | |forever to do| | |
| | | |something | | |
| | | |which won't | | |
| | | |succeed. Or | | |
| | | |if soft real | | |
| | | |time | | |
| | | |constraints | | |
| | | |are present, | | |
| | | |a result | | |
| | | |might be | | |
| | | |worthless | | |
| | | |altogether | | |
| | | |after some | | |
| | | |time). A | | |
| | | |sane default | | |
| | | |is probably | | |
| | | |30 seconds, | | |
| | | |although this| | |
| | | |depends | | |
| | | |heavily on | | |
| | | |the scenario | | |
| | | |and should be| | |
| | | |given a | | |
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| | | |thought | | |
| | | |during | | |
| | | |development. | | |
| | | |If the | | |
| | | |execution is | | |
| | | |terminated by| | |
| | | |this timeout,| | |
| | | |it should | | |
| | | |exit with | | |
| | | |state UNKNOWN| | |
| | | |(3) and (if | | |
| | | |possible) | | |
| | | |give some | | |
| | | |helpful | | |
| | | |output in | | |
| | | |which stage | | |
| | | |of the | | |
| | | |execution the| | |
| | | |timeout | | |
| | | |occurred. | | |
+----------+---------+---------------+-------------+--------+-----------+
|--hostname|-H |String, meaning|If the |yes |no |
| | |either a DNS |Monitoring | | |
| | |nameor an IP |Plugin | | |
| | |address of the |targets | | |
| | |targeted system|exactly one | | |
| | | |other system | | |
| | | |on the | | |
| | | |network, this| | |
| | | |option should| | |
| | | |be used to | | |
| | | |tell it which| | |
| | | |one. If the | | |
| | | |Monitoring | | |
| | | |Plugin does | | |
| | | |its test just| | |
| | | |locally or | | |
| | | |the logic | | |
| | | |does not | | |
| | | |apply to it, | | |
| | | |this option | | |
| | | |is, of | | |
| | | |course, | | |
| | | |optional. | | |
+----------+---------+---------------+-------------+--------+-----------+
|--verbose |-v |None |Increases the|yes |yes |
| | | |verbosity of | | |
| | | |the output, | | |
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| | | |thereby | | |
| | | |breaking the | | |
| | | |suggested | | |
| | | |rules about a| | |
| | | |short and | | |
| | | |concise | | |
| | | |output. The | | |
| | | |intention is | | |
| | | |to provide | | |
| | | |more | | |
| | | |information | | |
| | | |to a user. | | |
+----------+---------+---------------+-------------+--------+-----------+
|--exit-ok | |The Monitoring |yes |no | |
| | |Plugin exits | | | |
| | |unconditionally| | | |
| | |with OK (0). | | | |
| | |Mostly useful | | | |
| | |for the purpose| | | |
| | |of packaging | | | |
| | |and testing | | | |
| | |plugins, but | | | |
| | |might be used | | | |
| | |to always | | | |
| | |ignore errors | | | |
| | |(e.g. to just | | | |
| | |collect data). | | | |
+----------+---------+---------------+-------------+--------+-----------+
Table 2
3.1. Examples
For the execution with --help:
$ my_check_plugin --help
the output might look like this:
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my_check_plugin version 3.1.4
Licensed under the AGPLv1.
Repository: git.example.com/jdoe/my_check_plugin
This plugin just says hello. It fails if you don't give it a name.
Usage:
my_check_plugin --name NAME [--greeting GREETING]
Options:
--help
this help
--version
Shows the version of the plugin
--name NAME
if given, uses NAME as a name to greet.
--greeting GREETING
if given, uses GREETING instead of Hello.
Examples:
$ my_check_plugin --name Jane
Hello Jane
$ my_check_plugin --greeting Ciao --name Alice
Ciao Alice
This imaginary Monitoring Plugin tries to be really helpful here,
displays the version, the license and the upstream repository with
the help (although not necessary), has a short description about the
purpose, lists the options in an easily readable way and even gives
some examples.
For the execution with --version
$ my_check_plugin --version
the output might be a bit shorter:
my_check_plugin version 3.1.4
or even:
3.1.4
where both show the necessary information.
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4. Output of a Monitoring Plugin
The output of a Monitoring Plugin consists of two parts on the first
level, the _Exit Code_ and output in textual form on _stdout_.
4.1. Exit Code
The Monitoring Plugin MUST make use of the _Exit Code_ as a method to
communicate a result to the Monitoring System. Since the _Exit Code_
is more or less standardized over different systems as an integer
number with a width of or greater than 8bit, the following mapping is
used:
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+=============+==========+=========================================+
| Exit Code | Meaning | Meaning (extended) |
| (numerical) | (short) | |
+=============+==========+=========================================+
| 0 | OK | The execution of the Monitoring Plugin |
| | | proceeded as planned and the tests |
| | | appeared to function properly and the |
| | | measured values are within their |
| | | respective thresholds |
+-------------+----------+-----------------------------------------+
| 1 | WARNING | The execution of the Monitoring Plugin |
| | | proceeded as planned and the tests |
| | | appeared to _not_ function properly or |
| | | the measured values are _not_ with |
| | | their respective thresholds. The |
| | | problem(s) do(es) _not_ seem |
| | | exceptionally grave though and do(es) |
| | | _not_ require immediate attention |
+-------------+----------+-----------------------------------------+
| 2 | CRITICAL | The execution of the Monitoring Plugin |
| | | proceeded as planned and the tests |
| | | appeared to _not_ function properly or |
| | | the measured values are _not_ with |
| | | their respective thresholds. The |
| | | problem(s) _do(es)_ seem exceptionally |
| | | grave though and _do(es)_ require |
| | | immediate attention |
+-------------+----------+-----------------------------------------+
| 3 | UNKNOWN | The execution of the Monitoring Plugin |
| | | _did not_ proceed as planned. The |
| | | reasons might be manifold, e.g. missing |
| | | permissions, missing libraries, no |
| | | available network connection to the |
| | | destination, etc.. In summary: The |
| | | Monitoring Plugin could _not_ determine |
| | | the state of whatever it should have |
| | | been checking and can therefore make no |
| | | reliable statement about it. |
+-------------+----------+-----------------------------------------+
| 4-125 | reserved | |
| | for | |
| | future | |
| | use | |
+-------------+----------+-----------------------------------------+
Table 3
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4.2. Textual Output
The textual output should consist of printable characters end of this
output is marked by EOF. There is no length limitation per se, but
it a limit of 512kiB would be reasonable and should not be exceeded
to avoid influencing the performance of the monitoring system, also
some system might limit the output arbitrarily.
The original purpose of the output on _stdout_ was to provide
information for the user of the Monitoring System in a free text
form; a way for the Monitoring Plugin to communicate further details
on what happened and what the current state is. This purpose still
exists, but was expanded with the, so called, performance data to
allow the machine readable communication of measured values for
further processing in the Monitoring System, e.g. for the creation of
diagrams.
Therefore the further explanation is split into _free form output_
and _performance data_. The general schema is the following:
output = free-form-part *1( separator performance-data )
separator = "|"
unicode-without-separator = %x0A-7B / %x7D-10FFFF ; UTF-8 encoded unicode code point without "|"
free-form-part = *unicode-without-separator
labelchar = %x0A-1f / %x21-10FFFF ; UTF-8 encoded unicode code point without " "
labelstring-with-space = labelchar ( " " / labelchar ) labelchar ; no spaces at beginning or end
label = 1*labelchar / "'" labelstring-with-space "'" ; if the label contains spaces, surround it with '
UOM = 1*CHAR ; unit of measurement, a common unit specifier like "B" for Bytes or "s" for seconds
warning-value = range-expression
critical-value = range-expression
min-value = NUMERAL
max-value = NUMERAL
performance-data-value = label "=" NUMERAL *1( UOM ) *1( ";" *1warning_value *1( ";" *1critical-value *1( ";" *1min-value *1( ";" max-value ))))
performance-data = *performance-data-value *( " " performance-data-value )
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4.2.1. Free form output
This part of the output should give an user information about the
state of the test and, in the case of problems, ideally hint what the
origin of the problem might be or what the symptoms are. If the test
relies on numeric values, this might be displayed to give an user
more information about the specific problem. It might consist of one
or more lines (separated by CRLF or LF) of unicode symbols.
Considering the age and implementation of current systems,
restricting the output to US-ASCII characters is a safe choice.
Although no strict guidelines for creating this part of the output
can really be given due to its free form character, a developer
should keep a potential reader in mind. It might, for example, be OK
to put the output in a single line if there are only one or two items
of a similar type (think: multiple file systems, multiple sensors,
etc.) are present, but not if there 10 or 100, although this might
present a valid use case. If there are several different items
exists in the output of the Monitoring Plugin they probably SHOULD be
given their own line in the output.
The free form part is not intented for deep diagnostics, logging or
too detailed reports, therefore it should be kept rather short.
4.2.1.1. Examples
Remaining space on filesystem "/" is OK
Sensor temperature is within thresholds
Available Memory is too low
Sensore temperature exceeds thresholds
are OK, but
Remaining space on filesystem "/" is OK ( 62GiB / 128GiB )
Sensor temperature is within thresholds ( 42°C )
Available Memory is too low ( 126MiB / 32GiB )
Sensor temperature exceeds thresholds ( 78°C > 70°C )
are better.
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4.2.2. Performance data
In addition to the free form part the output can contain machine
readable measurement values.
In addition to the format definition earlier, the following contains
some constaints and best practices:
1. label MUST consist of at least one non-space character, but can
otherwise contain any printable characters except for the equals
sign (=) or single quotes ('). If it contains spaces, it must be
surrounded by single quotes
2. value is a numerical value, might be either an integer or a
floating point number. Using floating point numbers if the value
is really discreet SHOULD be avoided. The representation of a
floating point number SHOULD NOT use the "scientific notation"
(e.g. 6.02e23 or -3e-45), since some systems might not be able to
parse them correctly. Values with a base other then 10 SHOULD be
avoided (see below for more information on Byte values).
3. UOM is the _Unit of measurement_ (e.g. "B" for _Bytes_, "s" for
seconds) which gives more context to the Monitoring System.
* The following constraints MUST be applied:
1. An UOM of % MUST be used for percentage values
2. An UOM of c MUST be used for continuous counters (commonly
used for the sum of bytes transmitted on an interface)
* The following recommendations SHOULD be applied:
1. The UOM for Byte values is B and although many systems do
understand units like KB,KiB, MB, GB, TB they SHOULD be
avoided, at the least to avoid the ugly hassle about
people misinterpreting the _base10_ values as _base2_
values and the other way round. This is also a prime
example where floating point number SHOULD NOT be used,
since there are obviously only integer numbers included.
2. The UOM for time is s, meaning seconds, SI-Prefixes (e.g.
ms for milli seconds) are allowed if necessary or useful.
3. In general, SI units and SI prefixes MAY be used as UOM if
applicable, but the Monitoring System may not understand
them correctly (mostly in uncommon cases), in that cases
appropriate workarounds MAY be applied on the side of the
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Monitoring Plugin. Since the values are not intented to
be human readable, normalized units are recommended (e.g.
overall_power=14000000000W instead of overall_power=14GW)
4. warn and crit are the threshold values for this
measurement, which may have been given by the user as
input, may be hardcoded in the Monitoring Plugin or may be
retrieved from a file or a device or somewhere else during
the execution of the Monitoring Plugin. The unit used
MUST be the same as for _value_. These values are not
simple numbers, but range expressions (Section 2.1).
5. min and max are the minimal respectively the maximal value
the value could possibly be. The unit MUST be the same as
for value. These values can be omitted, if the value is a
percentage value, since min and max are always 0 and 100
in this case.
5. Implementation Status
The interface metioned here is implemented by several network
monitoring systems. A non-exhaustive list of these systems includes:
* Icinga 2
* Naemon
* Nagios
The other side of the interface is implemented by several different
projects, again in an non-exhaustive list:
* The Monitoring Plugins Project
* The Nagios Plugins Project
* The Linuxfabrik Monitoring Plugins
* Madrisan Nagios Plugins
6. Security Considerations
Special security considerations are hard to define regarding this
topic. Regarding the implementation of this interface, the usual
programming security considerations should apply (e.g. sanitize
inputs), but the risks and problems regarding security are dependent
on the specific implementation and usage.
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7. IANA Considerations
This document has no IANA actions.
8. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
Acknowledgments
Thanks for previous have to be said to the original inventors of this
interface, although it is not easy to determine who these persons
are, so they are mentioned here in general.
Thanks are going also to the many different implementors on either
side of this interface for their hard work which allows the use of
different components and systems with each other in the best spirit
of free software.
Author's Address
Lorenz Kästle
The Monitoring Plugins Project
Email: lorenz@vulgrim.de
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