Implements per-interface engaged alert upon alert drops

scripts/plugins/alerts/internals/alerts_drops/user_scripts/interface/dropped_alerts.lua

@@ -0,0 +1,53 @@
+--
+-- (C) 2019-20 - ntop.org
+--
+
+local user_scripts = require("user_scripts")
+local alerts_api = require("alerts_api")
+local alert_consts = require("alert_consts")
+
+local script = {
+  -- Script category
+  category = user_scripts.script_categories.internals,
+
+  -- This script is only for alerts generation
+  is_alert = true,
+
+  -- See below
+  hooks = {},
+
+  gui = {
+    i18n_title = "internals.alert_drops",
+    i18n_description = "internals.alert_drops_descr",
+  },
+}
+
+-- #################################################################
+
+local function dropped_alerts_check(params)
+   local dropped_alerts = interface.getStats()["num_dropped_alerts"]
+
+   -- Compute the delta with the previous value for drops
+   local delta_drops = alerts_api.interface_delta_val(script.key, params.granularity, dropped_alerts, true --[[ skip first --]])
+
+   local alert_type = alert_consts.alert_types.alert_dropped_alerts.create(
+      alert_consts.alert_severities.error,
+      alert_consts.alerts_granularities[params.granularity],
+      interface.getId(),
+      delta_drops
+   )
+
+   if(delta_drops > 0) then
+      alerts_api.trigger(params.alert_entity, alert_type, nil, params.cur_alerts)
+   else
+      alerts_api.release(params.alert_entity, alert_type, nil, params.cur_alerts)
+   end
+end
+
+-- #################################################################
+
+script.hooks.min = dropped_alerts_check
+
+-- #################################################################
+
+return script