core: instance restart (reload) event (#2178)

plugins.go

@@ -263,9 +263,10 @@ type EventName string
 // Define names for the various events
 const (
 	StartupEvent         EventName = "startup"
-	ShutdownEvent        EventName = "shutdown"
-	CertRenewEvent       EventName = "certrenew"
-	InstanceStartupEvent EventName = "instancestartup"
+	ShutdownEvent                  = "shutdown"
+	CertRenewEvent                 = "certrenew"
+	InstanceStartupEvent           = "instancestartup"
+	InstanceRestartEvent           = "instancerestart"
 )
 
 // EventHook is a type which holds information about a startup hook plugin.

sigtrap_posix.go

@@ -90,6 +90,7 @@ func trapSignalsPosix() {
 				purgeEventHooks()
 
 				// Kick off the restart; our work is done
+				EmitEvent(InstanceRestartEvent, nil)
 				_, err = inst.Restart(caddyfileToUse)
 				if err != nil {
 					restoreEventHooks(oldEventHooks)