xenial (7) smokeping_extend.7.gz

NAME

       smokeping_extend - Notes on extending Smokeping

OVERVIEW

       This document is intended to guide prospective authors in writing new Smokeping probes.  It mostly
       describes the interface between Smokeping and its probe modules. If it seems too complicated to
       understand, look at the existing modules for examples.

       Comments and proposed changes or additions are welcome.  Please send them to the smokeping-users mailing
       list. Patches against the POD source of this document are most appreciated.

CHOOSING A BASE CLASS

       The first thing you should decide is which base class you should use for your probe.  For most (if not
       all) uses it's a choice between Smokeping::probes::base and Smokeping::probes::basefork.  The former is
       intended for probes that can measure their targets all in one go, while the latter is for probing them
       one at a time, possibly in several concurrent subprocesses.

       At the moment, the only probes that use "Smokeping::probes::base" are the FPing derivatives. All the
       others use "Smokeping::probes::basefork", and chances are you should too. This document will thus
       concentrate on the latter case.

SKELETON FILE

       The Smokeping::probes::skel module is a non-functional probe that is intended to make a good basis for a
       new probe module. Copy the file, "lib/probes/skel.pm", to a new name and just fill out the blanks :) Note
       that the names of real probe modules must start with a capital letter.

PROBE DOCUMENTATION

       The probe documentation is generated from the source code with the smokeping arguments "--man" or
       "--makepod". The embedded POD documentation should point to this real documentation, so that curious
       users of the "perldoc" command see what's going on.  All the current probes do this.

       You should provide the method "pod_hash" that returns a reference to a hash with keys corresponding to
       the section names you want in the manpage. The supported section names are "name", "overview",
       "description", "authors", "notes", "bugs", and "see_also". If you don't need a particular section, just
       leave it out.

       The special sections "synopsis" and "variables" are automatically generated from the description of your
       variables. See below.

       Note that if you use 'here documents' ('<<') that have POD markup inside, you should escape the markup so
       that it doesn't show up in the embedded POD documentation. Most probes do it like this:

        my $e = "=";
        my $doc = <<DOC;
        ${e}head1 SECTION TITLE
        DOC

PROBE DESCRIPTION

       The probe should offer the "ProbeDesc" method that returns a short description of what it does. This will
       be used in the graphs produced by the web frontend.

VARIABLES

       All Smokeping probes must define their variables by implementing a "probevars" method for probe-specific
       variables and a "targetvars" method for target-specific variables. If you don't know the difference
       between these yet, see smokeping_examples.

       (The probes that are derived from "Smokeping::probes::base" don't support target-specific variables, so
       they only use the "probevars" method.)

       The base classes offer these methods too to provide the variables that are common to all the probes (eg.
       the probe-specific "step" variable and the target-specific "pings" variable. If you don't want to add
       anything to the base class variables (perhaps because all your variables are of a target-specific nature,
       so you don't need new probe-specific variables at all), you can leave the corresponding method out and it
       will be inherited from the base class.

       When you do supply your own "probevars" or "targetvars" method, you should combine your variables with
       those coming from the superclass. There is a convenience method called "_makevars" that does this, and
       the common idiom is

        sub probevars {
               my $class = shift;
               return $class->_makevars($class->SUPER::probevars, {
                       # your variables go here
               }
        }

       The variables are declared in a syntax that comes from the module used for parsing the configuration
       file, "Config::Grammar". Each variable should be a hash that uses the "special variable keys" documented
       in Config::Grammar. See "Smokeping::probes::skel" and the other probes for examples.

       For reference, here are the keys the hash should have. Much of this is taken straight from the
       "Config::Grammar" manual.

       Keys you must provide
           _doc
               Description of the variable.

           _example
               An example value. This will be used in the SYNOPSIS section in the probe manual.

       Optional keys
           _default
               A default value that will be assigned to the variable if none is specified or inherited.

           _re Regular expression upon which the value will be checked.

           _re_error
               String containing the returned error in case the regular expression doesn't match (if not
               specified, a generic 'syntax error' message will be returned).

           _sub
               A function pointer. It is called for every value, with the value passed as its first argument. If
               the function returns a defined value it is assumed that the test was not successful and an error
               is generated with the returned string as content.

       The "probevars" and "targetvars" methods should return hash references that contain the variable names as
       keys and the hashes described above as values. In addition the "Config::Grammar" special section key
       "_mandatory" is supported and should contain a reference to a list of mandatory variables. The
       "_makevars" method is aware of this special key and merges the mandatory lists in its arguments. Note
       that no other "Config::Grammar" special section keys are supported.

INITIALIZATION

       If you must do something at probe initialization time, like check that the external program you're going
       to use behaves as you expect, you should do it in the "new" method. You should probably also take care
       that you don't run the tests needlessly while in CGI mode. The usual way to do this is to test for
       $ENV{SERVER_SOFTWARE}. See the "Smokeping::probes::skel" module for an example.

PINGING

       All the real action happens in the "pingone" method (or, for "Smokeping::probes::base"-derived probes, in
       the "ping" method.) The arguments for "pingone" are $self, the module instance (since this is a method)
       and $target, the target to be probed.

       You can access the probe-specific variables here via the "$self->{properties}" hash and the target-
       specific ones via the "$target->{vars}" hash. You get the number of pings needed for the target via the
       "pings" method: "my $count = $self->pings($target)".

       You should return a sorted array of the latency times measured. If a ping fails, don't put anything in
       the array.

       That's it, you're done!

EXAMPLE CONFIGURATIONS

       If you would like to provide a documented example configuration for your probe (in addition to the
       automatically generated SYNOPSIS section in the probe manual), you can do so by adding it to the
       Smokeping::Examples module.  Look for the 'examples' subroutine and add your example there.

       Future versions of Smokeping might provide a way to embed examples in the probe modules too. The author's
       motivation for implementing this would be greatly increased by even a single demand for it, so please
       speak up if you think you'd use it.

TIMEOUT HANDLING

       If you deal with timeouts (for example because your program offers a parameter for specifying the timeout
       for the pings), you should know a few things.

       First, there's timeout logic in "Smokeping::probes::basefork" that kills the probe when the timeout is
       reached. By default the timeout is (# of pings * 5 seconds) + 1 second. If you expect that your pings can
       take longer, you should modify the default value of the probe-specific variable "timeout".  This would be
       done like this:

        sub probevars {
               my $class = shift;
               my $h = $class->SUPER::probevars;
               $h->{timeout}{_default} = 10; # override the superclass default
               return $class->_makevars($h, {
                       # your variables go here
               }
        }

       If you want to provide a target-specific "timeout" setting, you should delete the probe-specific variable
       and be sure to provide a default for your target-specific one. See eg. "Smokeping::probes::AnotherDNS"
       for an example of how this is done.

       Providing a target-specific "timeout" will make the timeout in "Smokeping::probes::basefork" be (# of
       pings * the maximum timeout of all targets) + 1 second. The 1 second is added so that the own timeout
       logic of the probe has time to kick in even in the worst case (ie. all pings are lost) before
       "Smokeping::probes::basefork" starts killing the processes.

COPYRIGHT

       Copyright 2005 by Niko Tyni.

LICENSE

       This program is free software; you can redistribute it and/or modify it under the terms of the GNU
       General Public License as published by the Free Software Foundation; either version 2 of the License, or
       (at your option) any later version.

       This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
       the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
       License for more details.

       You should have received a copy of the GNU General Public License along with this program; if not, write
       to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

AUTHOR

       Niko Tyni <ntyni@iki.fi>

BUGS

       This document makes writing new probes look much harder than it really is.

SEE ALSO

       The other Smokeping documents, especially smokeping_config.