I have a promise that defines a class if it succeeds in fetching data
from another system and writing that data to a local file:
"fetched_asset_data" expression => returnszero(
"$(dg.asset_command) -o $(dg.asset_cache_file) data $(sys.uqhost)",
"noshell"
);
I would like this promise to be evaluated in two situations. The first
is when the file /var/classes/force_asset_fetch is detected. A class
matching the filename is created and the file is deleted. The above
promise should run if that class is defined. This is an exceptional
case, however, used when an admin just made a change to the asset
database and wants Cfengine on that host to know about the change
immediately.
The main times this promise should run is basically once in a 12 hour
period, or twice a day roughly. This is just based upon historical
expectations for how often assets get updated in the database and is
probably even more frequent than really needed, but across all of our
systems it is probably a good balance.
So I was thinking of adding "action => if_elapsed_12_hours" to the
promise, where I have the body:
body action if_elapsed_12_hours {
ifelapsed => "720";
}
So ultimately, I would like this promise to run if 12 hours has elapsed
since it last ran (though I don't care when during the 12 hours) OR if
the force_asset_fetch class is defined. I just can't figure out how to
write the complete promise that combines both controlling factors. Any
suggestions?
UPDATE:
Right before sending this, I thought of an idea as I was skimming the
reference manual and remembering how Mark once explained something. I
figured I'd leave the above explanation in case anyone has an easy
answer to it, but "dist" classes may be the better way to go for this
problem!
Suppose I create a class promise called "percent_dist" and define it
this way:
classes:
"percent_dist" dist => { "1", "99" };
On a default schedule, cf-agent runs every 5 minutes, or 288 times per
day. The class random_dist_1 will be defined about 1% of the time
(1/(1+99)) and the class random_dist_99 will be defined 99% of the time
(99/(1+99)). So random_dist_1 would be defined about 2 to 3 times per
day! My promise condition then becomes
percent_dist_1|force_asset_fetch::
I could always tweak the percent_dist rlist if I want additional such
classes for other purposes, e.g. { "1", "10", "89" } to get a
percent_dist_10 class 10% of the time. The rlist values don't have to
total 100, it's just a convenience.
If someone wants to check my logic here, I'd appreciate it, but I think
I've answered my own question. :)
Justin
--
Justin C. Lloyd
Unix Infrastructure Engineer
DigitalGlobe, An Imaging and Information Company
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