Active Discovery and instance deletion

On 5/29/2020 at 9:35 AM, The Other Josh said:

Currently, if you configure instances to delete automatically it will prevent any alarms (the instance doesn't exist any more).  At first, support told me to 'delete after 30 days', which makes sense at a quick glance, but doesn't actually work; the instance doesn't exist, so there is no incoming data and hence no alerts to trigger.  The 30 days is just a way to preserve data in case the instance comes back (failed hardware, or intermittent service, etc).

That's exactly the reason for this feature. The other reason is that in case the instance comes back, it just shows up as a hole in data instead of losing historical data and resuming as a "new" instance.

On 5/29/2020 at 9:35 AM, The Other Josh said:

This means that you cannot enable automatic deletion for any instance where you need to alert on a change that would result in it being filtered from active discovery.

That's right. If an object has 4 states and you need to monitor for two of those states, those two states shouldn't be used as discovery filters, period. You'd need to find another attribute you can use to filter interfaces. AdminStatus is probably the best one for programmatically distinguishing between interfaces that are down on purpose vs. those that are accidentally down.

Theoretical rambling (needs to be thoroughly thought through):
You could get fancy and create an automatic aging property to exclude them from discovery X days after the inactive state is reached. On the first discovery cycle where the instance is down, you could set a timestamp in a property. The discovery script could check for the presence of this property and exclude the instance from the discovery output if the difference between property's value and now is greater than X days (which X could also be set as a property). This would allow alarming on an instance for X days after it goes down, then exclude it from discovery. Since the old interfaces DS uses SNMP as the collector, you'd have to switch over to a scripted DS. I think there is one coming out soon (or already available?) that is scripted to help with performance on very large devices. The property would likely need to be a device level property as a list of key/value pairs since 'instanceProps.get()' doesn't work (or does it?) in batchscript.