Hi @Dan Alan
You can use Site to Site reporting task to export NiFi metrics from one NiFi to another. You can set a SiteToSiteBulletinReportingTask and SiteToSiteStatusReportingTask at each edge NiFi and make them send data to a central NiFi.
On the central NiFi, you receive metrics as Json file in central NiFi and you can use any NiFi processor to analyse these events and extract the information that you need for your monitoring.
You can also use S2S Provenance RT is this is of interest
Is this what you are looking for ?