#  devdiscover.pod - Guide to devdiscover
#  Copyright (C) 2003 Shawn Ferry, Stanislav Sinyagin
#
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# $Id: devdiscover.pod,v 1.1 2010-12-27 00:04:36 ivan Exp $
# Shawn Ferry <sferry at sevenspace dot com> <lalartu at obscure dot org>
# Stanislav Sinyagin <ssinyagin@yahoo.com>
#

=head1 Torrus SNMP Device Discovery Developer's Guide

=head2 C<devdiscover> overview

C<devdiscover> is an extensible, module based, SNMP device discovery
utility. It is intended to automatically generate Torrus configuration
files, based on SNMP discovery results and templates.

See I<Torrus Command Reference> for command usage and functionality overview.

In general, C<devdiscover> consists of the following files and functional
parts:

=over 4

=item * C<bin/devdiscover.in>

This file is installed as C<bin/devdiscover> in Torrus installation directory,
with certain variables substituted. The program provides all the commandline
functionality and options processing. Once the CLI options are processed and
verified, the control is passed to the C<Torrus::DevDiscover> object.

=item * C<Torrus::DevDiscover>

This Perl module is responsible for the SNMP discovery process organization:

=over 8

=item *

it registers the discovery modules;

=item *

establishes an SNMP session to the target host;

=item *

initiates a new C<Torrus::DevDiscover::DevDetails> object for the target host;

=item *

stores the connection-specific parameters to the device object;

=item *

for each registered discovery module, executes C<checkdevtype()> in
I<sequential> order;

=item *

for those discovery modules which paid interest in this target host,
executes C<discover()> in I<sequential> order;

=item *

upon request from C<bin/devdiscover>, builds the configuration
XML tree, by calling C<buildConfig()> in I<sequential> order for each
relevant discovery module for each target host.

=back

=item * C<Torrus::DevDiscover::DevDetails>

This Perl module is defined in F<perllib/Torrus/DevDiscover.pm>, and provides
the functionality to store the results of SNMP device discovery.

=item * C<Torrus::ConfigBuilder>

This module is an encapsulation wrapper for XML configuration builder.
It provides methods for every element of Torrus configuration.

=item * Discovery Modules

These provide all the functionality for SNMP discovery. Normally
one module covers one MIB, or sometimes several vendor-specific MIBs,
and it is responsible for finding out the device details necessary
for Torrus configuration building. Usually a discovery module refers to one or
several I<template definition files>. A module may depend on
other modules' discovery results. This is controlled by its
C<sequence number>. Vendor-independent discovery modules are normally named
as C<Torrus::DevDiscover::RFCXXXX_SOME_HUMAN_NAME>, and vendor-specific
ones are named as C<Torrus::DevDiscover::Vendor[Product[Subsystem]]>.

=item * Template definition files

These are XML documents residing in F<xmlconfig/vendor> and
F<xmlconfig/generic> directories. Each file is a piece of Torrus configuration,
and contains definitions and templates for particular MIB or vendor.
Generic template definition files are for vendor-independent MIBs,
and normally they are named as F<rfcXXXX.some-human-name.xml>.
Vendor-specific files are named as F<vendor.product[.subsystem].xml>.

=back


=head2 Discovery Module Internals

Discovery modules are Perl packages with few required components.
Before creating your own modules, please read and follow
I<Torrus Programming Style Guide>.

Upon initialization, C<Torrus::DevDiscover> loads the modules listed in
C<@Torrus::DevDiscover::loadModules> array. This array is pre-populated
by standard module names in F<devdiscover-config.pl>.
You can add new module names by pushing them onto this array in your
local F<devdiscover-siteconfig.pl>.

=head3 Module Registration

Each discovery module should register itself in DevDiscover registry.
Normally there's only one registry entry per discovery module, though
it's not a limitation. The registry entry is identified by a registry
name, which normally repeats the module name.

Example:

    $Torrus::DevDiscover::registry{'RFC2790_HOST_RESOURCES'} = {
        'sequence'     => 100,
        'checkdevtype' => \&checkdevtype,
        'discover'     => \&discover,
        'buildConfig'  => \&buildConfig
        };

Each registry entry must contain 4 fields:

=over 4

=item * C<sequence>

The sequence number determines the order in which every discovery module's
procedure is executed. Sequence numbers of dependant modules must
be higher than those of their dependencies.

Generic MIB discovery modules should have the sequence number 100. If
a particular generic module depends on other generic modules, its sequence
number may be 110.

Vendor-specific modules should have the sequence number 500.
Vendor-specific modules that depend on other vendor-specific modules,
should have sequence number 510.

Dependencies deeper than one level may exist, but it's recommended
to avoid them. For most cases this should be enough.

Exception is made for C<RFC2863_IF_MIB> module, which has the sequence
number 50. That is because it provides the basic interface discovery,
and many other modules depend on its results.

Another exception is vendor-specific modules where the SNMP session parameters
must be set earliest possible. One of such parameters is C<snmp-max-msg-size>.
Some vendor SNMP agents would not be walked properly without this setting.
In these occasions, the sequence number is below 50. The recommended value
is 30.

=item * C<checkdevtype>

Must be a subroutine reference. This subroutine is called with two object
references as arguments: C<Torrus::DevDiscover> and
C<Torrus::DevDiscover::DevDetails>.
The purpose of this subroutine is to determine if the target host is
of required type, or if it supports the required MIB.
The subroutine should return true if and only if the target host
supports the MIB variables this module is supposed to discover. 

In general, C<checkdevtype> subroutine is small, and checks one or several
OIDs presence on the host, or their values, e.g. the value of I<sysObjectID>
variable. It should perform as less as possible SNMP requests, in order to
speed up the pre-discovery process.

=item * C<discover>

Must be a subroutine reference. This subroutine is called with the same
two arguments as C<checkdevtype()>. It is called for those modules only,
whose C<checkdevtype()> has returned true. The subroutine should return true
if no errors occured during the discovery.

The purpose of C<discover()> is to perform the actual SNMP discovery,
and prepare the parameter values for future XML configuration.

=item * C<buildConfig>

Must be a subroutine reference. This subroutine is called with three object
references as arguments: C<Torrus::DevDiscover::DevDetails>,
C<Torrus::ConfigBuilder>, and an XML element object, which should be used only
to pass data to ConfigBuilder methods.

This subroutine is designed to construct the resulting XML configuration
subtree as a child of a given XML element. Upper level subtrees
are handled by CLI options processing code.

=back


=head3 OID Definitions

OID definitions are designed to provide symbolic names to OIDs
in numerical notation. Normally the symbolic names repeat the names from
corresponding MIBs.

The definitions must be defined in an C<oiddef> hash defined in the
package namespace. Then they are automatically imported by DevDiscover
initialization procerure.

Example:

    our %oiddef =
        (
         'hrSystemUptime'               => '1.3.6.1.2.1.25.1.1.0',
         'hrSystemNumUsers'             => '1.3.6.1.2.1.25.1.5.0',
         'hrSystemProcesses'            => '1.3.6.1.2.1.25.1.6.0',
         'hrSystemMaxProcesses'         => '1.3.6.1.2.1.25.1.7.0',
         'hrMemorySize'                 => '1.3.6.1.2.1.25.2.2.0',
         'hrStorageTable'               => '1.3.6.1.2.1.25.2.3.1',
         'hrStorageIndex'               => '1.3.6.1.2.1.25.2.3.1.1',
         'hrStorageType'                => '1.3.6.1.2.1.25.2.3.1.2',
         'hrStorageDescr'               => '1.3.6.1.2.1.25.2.3.1.3',
         'hrStorageAllocationUnits'     => '1.3.6.1.2.1.25.2.3.1.4',
         'hrStorageSize'                => '1.3.6.1.2.1.25.2.3.1.5',
         'hrStorageUsed'                => '1.3.6.1.2.1.25.2.3.1.6',
         'hrStorageAllocationFailures'  => '1.3.6.1.2.1.25.2.3.1.7'
         );


=head3 Template References

Normally a discovery module would refer to configuration templates
defined in template definition files. In order to provide an extra level of
flexibility, these templates should be defined in
F<devdiscover-config.pl> or in F<devdiscover-siteconfig.pl>.

It is recommended that the template references in the discovery modules
follow the naming standard: C<module::template-name>.

ConfigBuilder's C<addTemplateApplication()> method looks up every
template name in the global hash C<%Torrus::ConfigBuilder::templateRegistry>
and figures out the source XML file and the actual template name.

Example:

    $Torrus::ConfigBuilder::templateRegistry{
        'RFC2790_HOST_RESOURCES::hr-system-uptime'} = {
            'name'   => 'mytest-hr-system-uptime',
            'source' => 'mytest.templates.xml'
            };


=head3 Interface filtering

Usually not all interfaces from ifTable need to be monitored.
For example, Loopback and Null0 interfaces on Cisco routers.

C<Torrus::DevDiscover::RFC2863_IF_MIB> provides the functionality to
automatically filter out the interfaces, based on filter definitions.
Filter definitions are registered by calling the subroutine
C<Torrus::DevDiscover::RFC2863_IF_MIB::addInterfaceFilter
($devdetails, $interfaceFilter)>. The second argument is a reference
to a hash of the following structure:

Keys are symbolic names that mean nothing and need only to be unique.
Values are hash references with the following entries: C<ifType>
specifies the IANA interface type, and optional C<ifDescr> specifies
a regular expression to match against interface description.

The filters are usually registered within C<checkdevtype> subroutine
of the vendor module, after the device type is identified. See
F<CiscoIOS.pm> and F<CiscoCatOS.pm> as examples.


=head2 Authors

Shawn Ferry: initial draft.

Stanislav Sinyagin: revision and detailed content.