15. Anatomy of a Module

Each module inherits (@ISA = ("Module_Template");) from _Modules/Module_Template.

15.1. Module_Template.pm

sub template

Called by each module constructor (e.g., Mon_Processes::new):

• ensures pointers to base-modules configuration, application output streams and the date-time stamp have all been passed through;
  
  
• sets the default OUTPUT_MODES, currently to "Local", implemented by _Mods_Out/Out_Local (this value is often overridden to "NONE" in modules which collect no data of their own, i.e., provide data for application stream only);
  
  
• sets the default configuration for the monitoring module's own output streams — Local Logs — should they exist, which can be overridden in the module constructor;
  
  
• grabs the output streams configuration from ModsConfig --- this takes priority over both the config in the module's construction (new) and that within the template;
  
  
• copies the config to std_log_echo;

Simple read methods: sub stream_config last_data_write_time and name

Simple write methods: sub set_last_data_write_time

sub init_output_modes

Initialise our own (not application) output streams, e.g., open files.

maintain_logs

Maintain our own (not application) output streams, e.g., rotate files.

sub data

Get data from the operating system, usually with the help of something from LocalConfig.

sub tick, warnings_scan and sub trouble_scan

Default methods for sending output to the application output streams — these are usually overridden: such methods often grab data via LocalConfig and scan it for things of interest, before sending messages to the appropriate application streams.

15.2. Typical Module

sub new

• Sets default configuration for its own output streams (which override those set in Module_Template::template, but are overridden by those set in ModsConfig — the latter being grabbed in the call (below) to Module_Template::template.
  
  
• Possibly overwide the default setting for our own output streams (default is set in Module_Template::template), e.g. $self->{STREAMS} = "NONE" if we are a monitoring-only module (have no output streams of our own) and then initialise these output streams (init_output_streams).

sub data

Possibly override method inherited from Module_Template for grabbing some data from the operating-system (probably with help from LocalConfig).

sub tick, warnings_scan and trouble_scan

Possibly override methods from Module_Template for grabbing data from the OS, (for warnings and trouble) scanning for things of interest, and sending messages to the application output streams.