GROK Filter - Extract Year and Month

[JeremyP]

Hi.... I'm looking for some help on creating a new field based on a grok pattern.

Here is the field in question:

"last_assessed_for_vulnerabilities": "2021-12-10T07:05:41.154Z"

I'm looking to create the following field using the year and month date...

report_period : 2021-12

I'm close, but I can't seem to get GROK to process the month properly. Any help is appreciated!

[Badger]

How about

grok {
    pattern_definition => { "MYDATE" => "%{YEAR}-%{MONTHNUM}" }
    match => { "last_assessed_for_vulnerabilities" => "^%{MYDATE:someFeild}" }
}