Alerting

Create alert when average events greater than 2 standard deviations from rolling average

jodros
Builder

I know that there are several threads on answers that reference alerts based on standard deviation. I have tried a few of them and the use cases do not seem to meet what I need.

I would like to create an alert that will fire when the average of events over 5 minutes is greater than 2 standard deviations of the average of events over 60 minutes. This post is the closest I have found, but I am still stuck.

https://answers.splunk.com/answers/227404/alert-when-sample-is-2-standard-deviations-from-mo.html?ut...

Any assistance would be appreciated.

Thanks

Tags (2)

tlagatta_splunk
Splunk Employee
Splunk Employee

Hi Jodros, check out the Security Essentials app, which goes through a lot of statistical use cases like this:

Security Essentials App:
https://splunkbase.splunk.com/app/3435/

For example, you can start from the "Sources Sending a High Volume of DNS Traffic" use case in the Security Essentials app. This query identifies hosts with very high traffic (more than 3 standard standard deviations). You should be able to adapt this to your use case:

| inputlookup dns_data_anon.csv 
| convert mktime(_time) timeformat="%Y-%m-%dT%H:%M:%S.%3Q%z" 
| bucket _time span=1h 
| stats sum(bytes*) as bytes* by src_ip _time 
| eventstats max(_time) as maxtime avg(bytes_out) as avg_bytes_out stdev(bytes_out) as stdev_bytes_out 
| eventstats count as num_data_samples avg(eval(if(_time < relative_time(maxtime, "@h"),bytes_out,null))) as per_source_avg_bytes_out stdev(eval(if(_time < relative_time(maxtime, "@h"),bytes_out,null))) as per_source_stdev_bytes_out by src_ip 
| where num_data_samples >=4 AND bytes_out > avg_bytes_out + 3 * stdev_bytes_out AND bytes_out > per_source_avg_bytes_out + 3 * per_source_stdev_bytes_out AND _time >= relative_time(maxtime, "@h") 
| eval num_standard_deviations_away_from_org_average = round(abs(bytes_out - avg_bytes_out) / stdev_bytes_out,2), num_standard_deviations_away_from_per_source_average = round(abs(bytes_out - per_source_avg_bytes_out) / per_source_stdev_bytes_out,2) 
| fields - maxtime per_source* avg* stdev*
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