Dave Josephsen's presentation on using writing event brokers for Nagios. The presentation was given during the Nagios World Conference North America held Sept 25-28th, 2012 in Saint Paul, MN. For more information on the conference (including photos and videos), visit: http://go.nagios.com/nwcna

1. Stop being lazy and write
an event broker module already
Dave Josephsen
dave@dbg.com

2. WHY?!
The NEB interface is AWESOME
Interpreted automata is expensive
Especially via global event handlers and/or
performance-data hooks
You're more likely to make something I can use
too!
2012 2

3. How we're going to do this
Function pointers (and YOU)
What is the event broker?
How do we use it?
A few words of advice
Dissect a couple existing plugins
Nagfs
DNX
2012 3

4. Function Pointers are weird, but they make
callbacks possible
Normal Function Declarations
void main() {
int c2f ( int c ) { return (9/5) *c+32; }
int f2c ( int f ) { return (5/9) *(f-32); }
Argument
int convert (int input, int (*fPointer)(int)) {
return fPointer(input);
}
wha??
void Go() {
int result=convert('72',&f2c);
}
Oh.. ok.
}
2012 4

5. What is the event broker?
Event Broker added
Nagios Event loop
(kinda)
2012 5

6. How do we use it?
Write an init function
int nebmodule_init( int flags, char * args, nebmodule * handle)
Subscribe to the events you want
neb_register_callback(STUFF, handle, '1', &myhandler);
Write handler functions for each event you
subscribed to
int myhandler(int neb_event_type, nebstruct_stuff_data *ds)
Write a de-init function
int nebmodule_deinit(int flags, int reason){ return 0 }
2012 6

7. How do we use it? (cont)
include/nebcallbacks.h
NEBCALLBACK_RAW_DATA
NEBCALLBACK_NEB_DATA
NEBCALLBACK_PROCESS_DATA
NEBCALLBACK_TIMED_EVENT_DATA neb_register_callback(NEBCALLBACK_TIMED_EVENT_DATA, handle, '1', &handler);
NEBCALLBACK_LOG_DATA
NEBCALLBACK_SYSTEM_COMMAND_DATA
NEBCALLBACK_EVENT_HANDLER_DATA
NEBCALLBACK_NOTIFICATION_DATA
NEBCALLBACK_SERVICE_CHECK_DATA base/broker.c
NEBCALLBACK_HOST_CHECK_DATA
NEBCALLBACK_COMMENT_DATA /* fill struct with relevant data */
NEBCALLBACK_DOWNTIME_DATA
NEBCALLBACK_FLAPPING_DATA ds.type=type;
NEBCALLBACK_PROGRAM_STATUS_DATA ds.flags=flags;
NEBCALLBACK_HOST_STATUS_DATA ds.attr=attr;
NEBCALLBACK_SERVICE_STATUS_DATA
NEBCALLBACK_ADAPTIVE_PROGRAM_DATA ds.timestamp=get_broker_timestamp(timestamp);
NEBCALLBACK_ADAPTIVE_HOST_DATA
NEBCALLBACK_ADAPTIVE_SERVICE_DATA ds.event_type=event->event_type;
NEBCALLBACK_EXTERNAL_COMMAND_DATA
NEBCALLBACK_AGGREGATED_STATUS_DATA ds.recurring=event->recurring;
NEBCALLBACK_RETENTION_DATA ds.run_time=event->run_time;
NEBCALLBACK_CONTACT_NOTIFICATION_DATA ds.event_data=event->event_data;
NEBCALLBACK_CONTACT_NOTIFICATION_METHOD_DATA
NEBCALLBACK_ACKNOWLEDGEMENT_DATA ds.event_ptr=(void *)event;
NEBCALLBACK_STATE_CHANGE_DATA
NEBCALLBACK_CONTACT_STATUS_DATA /* make callbacks */
NEBCALLBACK_ADAPTIVE_CONTACT_DATA
neb_make_callbacks(NEBCALLBACK_TIMED_EVENT_DATA,(void *)&ds);
include/broker.h
#define NEBTYPE_TIMEDEVENT_ADD
#define NEBTYPE_TIMEDEVENT_REMOVE
#define NEBTYPE_TIMEDEVENT_EXECUTE int handler(int neb_event_type, nebstruct_timed_event_data *ds)
#define NEBTYPE_TIMEDEVENT_DELAY
#define NEBTYPE_TIMEDEVENT_SKIP
#define NEBTYPE_TIMEDEVENT_SLEEP
2012 7

8. How do we use it? (cont)
Everything is a struct
Every struct is globally scoped
The sky is the limit
enumerate/add/remove events from the queue
reconfigure hosts/services post-runtime
export/import data from/to whatever
process check data, inject/delete check results
GO CRAZY!
2012 8

9. Some words of advice
There's a “hello world” module in contrib
Write your thingy as a stand-alone thingy first, and
then convert it to an EH function
Start simple, and then build up
Avoid Threads
(run them in a separate process)
The DNX guys have pre-packaged the headers for
various versions of Nagios (zomgthankyou)
2012 9

10. Nagfs

11. DNX
●External process IPC
●Service check preemption
●Check result injection

12. OK BYE!
http://old.nagios.org/developerinfo/
http://nagios.larsmichelsen.com/event_broker_options/
http://dnx.sourceforge.net/
(and speaking of “buy”...)